Zoom lens system

ABSTRACT

A zoom lens system has, from the object side, a first lens unit, a second lens unit and a third lens unit. The first lens unit has a negative optical power as a whole. The second and third lens units have a positive optical power as a whole. In the zoom lens system, zooming is achieved by varying the distance between the first and second lens units, and at least one of the lens elements is a plastic lens element.

This disclosure is based on applications No. H10-363664 filed in Japanon Dec. 22, 1998 and No. H11-005056 filed in Japan on Jan. 12, 1999, theentire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom lens system, and moreparticularly to a compact and inexpensive zoom lens system particularlysuited for use in digital still cameras.

2. Description of the Prior Art

In recent years, as personal computers become more prevalent, digitalstill cameras that allow easy storage of image data on a recordingmedium such as a floppy disk have been coming into wider use. This trendhas created an increasing demand for more inexpensive digital stillcameras. This in turn has created an increasing demand for further costreduction in imaging optical systems. On the other hand, photoelectricconversion devices have come to have an increasingly large number ofpixels year by year, which accordingly demands imaging optical systemsthat offer higher and higher performance. To comply with suchrequirements, it is necessary to produce a high-performance imagingoptical system at comparatively low cost.

To achieve this objective, for example, Japanese Laid-open PatentApplications Nos. H1-183615 and H9-311273 propose optical systems havinga first lens unit of a negative-negative-positive configuration and asecond lens unit of a positive-negative-positive configuration.Moreover, the optical systems proposed in Japanese Laid-open PatentApplications Nos. H7-113956, H6-300969, and H7-63991 have a second lensunit including a doublet lens element formed by cementing togethernegative lens elements; and the optical system proposed in JapaneseLaid-open Patent Application No. H5-93858 has a second lens unitincluding a doublet lens element formed by cementing together, from theobject side, a positive lens element and a negative lens element. If adoublet lens element is considered to be a single lens element, it isassumed that those optical systems are each composed of a first lensunit of a negative-negative-positive configuration and a second lensunit of a positive-negative-positive configuration.

Furthermore, Japanese Laid-open Patent Applications Nos. H6-201993 andH1-191820 propose optical systems that are composed of a first lens unithaving a negative optical power, a second lens unit having a positiveoptical power, and a third lens unit having a positive optical power andemploy a plastic lens element.

In the optical systems proposed in the above-mentioned patentapplications, however, there is still plenty of room for improvementfrom the viewpoint of miniaturization, high performance, and costreduction.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a compact,high-resolution, and low-cost zoom lens system suitable, in particular,for use in a digital still camera by arranging plastic lens elementseffectively in a two-unit zoom lens system of a negative-positiveconfiguration.

To achieve the above object, according to one aspect of the presentinvention, a zoom lens system includes, from the object side, a firstlens unit and a second lens unit. The first lens unit is composed of anegative, a negative, and a positive lens element and has a negativeoptical power as a whole. The second lens unit is composed of apositive, a negative, and a positive lens element and has a positiveoptical power as a whole. In the zoom lens system, zooming is achievedby varying the distance between the first and second lens units, and atleast one of those lens elements is a plastic lens element.

According to another aspect of the present invention, a zoom lens systemincludes, from the object side, a first lens unit having a negativeoptical power and a second lens unit having a positive optical power. Inthe zoom lens system, zooming is achieved by varying the distancebetween the first and second lens units, and at least a negative lenselement and a positive lens element of the lens elements included in thelens units are plastic lens elements that fulfill the followingcondition:

−1.2<φPi/φW×hi<1.2

where

φW represents the optical power of the entire zoom lens system at thewide-angle end;

φPi represents the optical power of the ith plastic lens element; and

hi represents the height of incidence at which a paraxial ray enters theobject-side surface of the ith plastic lens element at the telephotoend, assuming that the initial values of the converted inclination α1and the height h1, for paraxial tracing, are 0 and 1, respectively.

According to another aspect of the present invention, an image takingapparatus is composed of a zoom lens system, a photoelectric conversiondevice, and an optical low-pass filter. The photoelectric conversiondevice has a light-sensing surface on which an image is formed by thezoom lens system. The optical low-pass filter is disposed on the objectside of the photoelectric conversion device. The zoom lens system iscomposed of, from the object side, a first lens unit and a second lensunit. The first lens unit is composed of a negative, a negative, and apositive lens element, and has a negative optical power as a whole. Thesecond lens unit is composed of a positive, a negative, and a positivelens element, and has a positive optical power as a whole. In the zoomlens system, zooming is achieved by varying the distance between thefirst and second lens units, and at least one of those lens elements isa plastic lens element.

According to another aspect of the present invention, a zoom lens systemis composed of, from the object side, a first lens unit, a second lensunit, and a third lens unit. The first lens unit has a negative opticalpower. The second lens unit is composed of at least a positive and anegative lens element, and has a positive optical power. The third lensunit has a positive optical power. In the zoom lens system, zooming isachieved by moving at least two lens units so as to vary the distancebetween the first and second lens units and the distance between thesecond and third lens units, and at least one of the lens elementsincluded in the lens units is a plastic lens element that fulfills thefollowing conditions:

−8.0<Cp×(N′−N)/φW<0.8

−0.45<M3/M2<0.09(whereφT/φW>1.6)

where

Cp represents the curvature of the plastic lens element;

φW represents the optical power of the entire zoom lens system at thewide-angle end;

N′ represents the refractive index of the object-side medium of theaspherical surface for the d line;

N represents the refractive index of the image-side medium of theaspherical surface for the d line;

M3 represents the amount of movement of the third lens unit (thedirection pointing to the object side is negative with respect to thewide-angle end);

M2 represents the amount of movement of the second lens unit (thedirection pointing to the object side is negative with respect to thewide-angle end); and

φT represents the optical power of the entire zoom lens system at thetelephoto end.

According to another aspect of the present invention, a zoom lens systemis composed of, from the object side, a first lens unit, a second lensunit, and a third lens unit. The first lens unit is composed of at leasta positive and a negative lens element, and has a negative opticalpower. The second and third lens units have a positive optical power. Inthe zoom lens system, zooming is achieved by moving at least two lensunits so as to vary the distance between the first and second lens unitsand the distance between the second and third lens units, and at leastone of the lens elements included in the first lens unit is a plasticlens element that fulfills the following conditions:

|φP/φ1|<1.20

0.20<|φ1/φW|<0.70

−0.45<M3/M2<0.90(whereφT/φW>1.6)

where

φP represents the optical power of the plastic lens element;

φ1 represents the optical power of the first lens unit;

φW represents the optical power of the entire zoom lens system at thewide-angle end;

M3 represents the amount of movement of the third lens unit (thedirection pointing to the object side is negative with respect to thewide-angle end);

M2 represents the amount of movement of the second lens unit (thedirection pointing to the object side is negative with respect to thewide-angle end); and

φT represents the optical power of the entire zoom lens system at thetelephoto end.

According to another aspect of the present invention, a zoom lens systemis composed of, from the object side, a first lens unit, a second lensunit, and a third lens unit. The first lens unit has a negative opticalpower. The second lens unit is composed of at least a positive and anegative lens element, and has a positive optical power. The third lensunit has a positive optical power. In the zoom lens system, zooming isachieved by varying the distance between the first and second lens unitsand the distance between the second and third lens units, and at leastone of the lens elements included in the second lens unit is a plasticlens element that fulfills the following conditions:

|φP/φ2|<2.5

0.25<φ2/φW<0.75

where

φP represents the optical power of the plastic lens element;

φ2 represents the optical power of the second lens unit; and

φW represents the optical power of the entire zoom lens system at thewide-angle end.

According to another aspect of the present invention, a zoom lens systemis composed of, from the object side, a first lens unit, a second lensunit, and a third lens unit. The first lens unit has a negative opticalpower. The second and third lens units have a positive optical power. Inthe zoom lens system, zooming is achieved by moving at least two lensunits so as to vary the distance between the first and second lens unitsand the distance between the second and third lens units, and at leastone of the lens elements included in the third lens unit is a plasticlens element that fulfills the following conditions:

 −0.30<M3/M2<0.90

|φP/φ3|<1.70

0.1<φ3/φW<0.60

where

M3 represents the amount of movement of the third lens unit (thedirection pointing to the object side is negative with respect to thewide-angle end);

M2 represents the amount of movement of the second lens unit (thedirection pointing to the object side is negative with respect to thewide-angle end);

φP represents the optical power of the plastic lens element;

φ3 represents the optical power of the third lens unit; and

φW represents the optical power of the entire zoom lens system at thewide-angle end.

According to another aspect of the present invention, a zoom lens systemis composed of, from the object side, a first lens unit, a second lensunit, and a third lens unit. The first lens unit has a negative opticalpower. The second and third lens units have a positive optical power. Inthe zoom lens system, zooming is achieved by moving at least two lensunits so as to vary the distance between the first and second lens unitsand the distance between the second and third lens units, and at leastone of the lens elements included in the first lens unit and at leastone of the lens elements included in the second lens unit are plasticlens elements that fulfill the following conditions:

−1.4<φPi/φW×hi<1.4

0.5<log(β2T/β2W)/logZ<2.2

where

φPi represents the optical power of the ith plastic lens element;

φW represents the optical power of the entire zoom lens system at thewide-angle end;

hi represents the height of incidence at which a paraxial ray enters theobject-side surface of the ith plastic lens element at the telephotoend, assuming that the initial values of the converted inclination α1and the height h1, for paraxial tracing, are 0 and 1, respectively;

β2W represents the lateral magnification of the second lens unit at thewide-angle end;

β2T represents the lateral magnification of the second lens unit at thetelephoto end;

Z represents the zoom ratio; and

log represents a natural logarithm (since the condition defines aproportion, the base does not matter).

According to another aspect of the present invention, a zoom lens systemis composed of, from the object side, a first lens unit, a second lensunit, and a third lens unit. The first lens unit has a negative opticalpower. The second lens unit is composed of at least a positive and anegative lens element, and has a positive optical power. The third lensunit has a positive optical power. In the zoom lens system, zooming isachieved by moving at least two lens units so as to vary the distancebetween the first and second lens units and the distance between thesecond and third lens units, and at least one of the lens elementsincluded in the first lens unit and at least one of the lens elementsincluded in the third lens unit are plastic lens elements that fulfillthe following conditions:

−1.4<φPi/φW×hi<1.4

−1.2<log(β3T/β3W)/logZ<0.5

where

φPi represents the optical power of the ith plastic lens element;

φW represents the optical power of the entire zoom lens system at thewide-angle end;

hi represents the height of incidence at which a paraxial ray enters theobject-side surface of the ith plastic lens element at the telephotoend, assuming that the initial values of the converted inclination a 1and the height h1, for paraxial tracing, are 0 and 1, respectively;

β3W represents the lateral magnification of the third lens unit at thewide-angle end;

β3T represents the lateral magnification of the third lens unit at thetelephoto end;

Z represents the zoom ratio; and log represents a natural logarithm(since the condition defines a proportion, the base does not matter).

According to still another aspect of the present invention, a zoom lenssystem is composed of, from the object side, a first lens unit, a secondlens unit, and a third lens unit. The first lens unit has a negativeoptical power. The second lens unit is composed of at least a positiveand a negative lens element, and has a positive optical power. The thirdlens unit has a positive optical power. In the zoom lens system, zoomingis achieved by moving at least two lens units so as to vary the distancebetween the first and second lens units and the distance between thesecond and third lens units, and at least one of the lens elementsincluded in the second lens unit and at least one of the lens elementsincluded in the third lens unit are plastic lens elements that fulfillthe following conditions:

 −1.4<φPi/φW×hi<1.4

−0.75<log(β3T/β3W)/log(β2T/β2W)<0.65

where

φPi represents the optical power of the ith plastic lens element;

φW represents the optical power of the entire zoom lens system at thewide-angle end;

hi represents the height of incidence at which a paraxial ray enters theobject-side surface of the ith plastic lens element at the telephotoend, assuming that the initial values of the converted inclination α1and the height h1, for paraxial tracing, are 0 and 1, respectively;

β2W represents the lateral magnification of the second lens unit at thewide-angle end;

β2T represents the lateral magnification of the second lens unit at thetelephoto end;

β3W represents the lateral magnification of the third lens unit at thewide-angle end;

β3T represents the lateral magnification of the third lens unit at thetelephoto end; and

log represents a natural logarithm (since the condition defines aproportion, the base does not matter).

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of this invention will become clear from thefollowing description, taken in conjunction with the preferredembodiments with reference to the accompanied drawings in which:

FIG. 1 is a lens arrangement diagram of the zoom lens system of a firstembodiment (Example 1) of the present invention;

FIG. 2 is a lens arrangement diagram of the zoom lens system of a secondembodiment (Example 2) of the present invention;

FIG. 3 is a lens arrangement diagram of the zoom lens system of a thirdembodiment (Example 3) of the present invention;

FIG. 4 is a lens arrangement diagram of the zoom lens system of a fourthembodiment (Example 4) of the present invention;

FIG. 5 is a lens arrangement diagram of the zoom lens system of a fifthembodiment (Example 5) of the present invention;

FIGS. 6A to 6I are graphic representations of the aberrations observedin an infinite-distance shooting condition in the zoom lens system ofExample 1;

FIGS. 7A to 7I are graphic representations of the aberrations observedin an infinite-distance shooting condition in the zoom lens system ofExample 2;

FIGS. 8A to 8I are graphic representations of the aberrations observedin an infinite-distance shooting condition in the zoom lens system ofExample 3;

FIGS. 9A to 9I are graphic representations of the aberrations observedin an infinite-distance shooting condition in the zoom lens system ofExample 4;

FIGS. 10A to 10I are graphic representations of the aberrations observedin an infinite-distance shooting condition in the zoom lens system ofExample 5;

FIG. 11 is a lens arrangement diagram of the zoom lens system of a sixthembodiment (Example 6) of the present invention;

FIG. 12 is a lens arrangement diagram of the zoom lens system of aseventh embodiment (Example 7) of the present invention;

FIG. 13 is a lens arrangement diagram of the zoom lens system of aneighth embodiment (Example 8) of the present invention;

FIG. 14 is a lens arrangement diagram of the zoom lens system of a ninthembodiment (Example 9) of the present invention;

FIG. 15 is a lens arrangement diagram of the zoom lens system of a tenthembodiment (Example 10) of the present invention;

FIG. 16 is a lens arrangement diagram of the zoom lens system of aneleventh embodiment (Example 11) of the present invention;

FIG. 17 is a lens arrangement diagram of the zoom lens system of atwelfth embodiment (Example 12) of the present invention;

FIG. 18 is a lens arrangement diagram of the zoom lens system of athirteenth embodiment (Example 13) of the present invention;

FIG. 19 is a lens arrangement diagram of the zoom lens system of afourteenth embodiment (Example 14) of the present invention;

FIGS. 20A to 20I are graphic representations of the aberrations observedin an infinite-distance shooting condition in the zoom lens system ofExample 6;

FIGS. 21A to 21I are graphic representations of the aberrations observedin an infinite-distance shooting condition in the zoom lens system ofExample 7;

FIGS. 22A to 22I are graphic representations of the aberrations observedin an infinite-distance shooting condition in the zoom lens system ofExample 8;

FIGS. 23A to 23I are graphic representations of the aberrations observedin an infinite-distance shooting condition in the zoom lens system ofExample 9;

FIGS. 24A to 24I are graphic representations of the aberrations observedin an infinite-distance shooting condition in the zoom lens system ofExample 10;

FIGS. 25A to 25I are graphic representations of the aberrations observedin an infinite-distance shooting condition in the zoom lens system ofExample 11;

FIGS. 26A to 26I are graphic representations of the aberrations observedin an infinite-distance shooting condition in the zoom lens system ofExample 12;

FIGS. 27A to 27I are graphic representations of the aberrations observedin an infinite-distance shooting condition in the zoom lens system ofthe Example 13;

FIGS. 28A to 28I are graphic representations of the aberrations observedin an infinite-distance shooting condition in the zoom lens system ofthe Example 14;

FIG. 29 is a lens arrangement diagram of the zoom lens system of afifteenth embodiment (Example 15) of the present invention;

FIGS. 30A to 30I are graphic representations of the aberrations observedin an infinite-distance shooting condition in the zoom lens system ofExample 15; and

FIG. 31 is a schematic illustration of the optical components of adigital camera.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments 1 to 5

Hereinafter, zoom lens systems embodying the present invention will bedescribed with reference to the drawings. FIGS. 1 to 5 are lensarrangement diagrams of the zoom lens systems of a first, a second, athird, a fourth, and a fifth embodiment, respectively. In each diagram,the left-hand side corresponds to the object side, and the right-handside corresponds to the image side. Note that, in each diagram, arrowsschematically indicate the movement of the lens units during zoomingfrom the wide-angle end to the telephoto end. Moreover, each diagramshows the lens arrangement of the zoom lens system during zooming, asobserved at the wide-angle end. As shown in these diagrams, the zoomlens systems of the embodiments are each built as a two-unit zoom lenssystem of a negative-positive configuration that is composed of, fromthe object side, a first lens unit Gr1 and a second lens unit Gr2. Boththe first and second lens units (Gr1 and Gr2) are movably disposed inthe zoom lens system.

The first lens unit Gr1 is composed of, from the object side, a negativelens element, a negative lens element, and a positive lens element andhas a negative optical power as a whole. The second lens unit Gr2 iscomposed of an aperture stop S, a positive lens element, a negative lenselement, and a positive lens element and has a positive optical power asa whole. In the zoom lens system, the first to sixth lens elementscounted from the object side are represented as G1 to G6, respectively.Note that a flat plate disposed at the image-side end of the zoom lenssystem is a low-pass filter LPF. As illustrated in FIG. 31, within adigital camera the low-pass filter LPF is disposed between the zoom lenssystem ZLS and a photoelectric image sensor IS having a light-sensingsurface on which an image is formed by the zoom lens system.

As shown in FIG. 1, in the first embodiment, the second and sixth lenselements (G2 and G6) counted from the object side (hatched in thefigure) are plastic lens elements. As shown in FIG. 2, in the secondembodiment, the second, third, fifth, and sixth lens elements (G2, G3,G5, and G6) counted from the object side (hatched in the figure) areplastic lens elements.

Moreover, as shown in FIG. 3, in the third embodiment, the second,fifth, and sixth lens elements (G2, G5, and G6) counted from the objectside (hatched in the figure) are plastic lens elements. As shown in FIG.4, in the fourth embodiment, the third and fifth lens elements (G3 andG5) counted from the object side (hatched in the figure) are plasticlens elements. Lastly, as shown in FIG. 5, in the fifth embodiment, thesecond and sixth lens elements (G2 and G6) counted from the object side(hatched in the figure) are plastic lens elements.

The conditions to be preferably fulfilled by an optical system will bedescribed below. It is preferable that the zoom lens systems of theembodiments fulfill Condition (1) below.

0.25<|φ1/φW|<0.80  (1)

where

φ1 represents the optical power of the first lens unit; and

φW represents the optical power of the entire zoom lens system at thewide-angle end.

Condition (1) defines, in the form of the optical power of the firstlens unit, the condition to be fulfilled to achieve proper correction ofaberrations and keep the size of the zoom lens system appropriate. Ifthe value of Condition (1) is equal to or less than its lower limit, theoptical power of the first lens unit is so weak that aberrations can becorrected properly, but simultaneously the total length, as well as thediameter of the front-end lens unit, of the zoom lens system becomesunduly large. In contrast, if the value of Condition (1) is equal to orgreater than its upper limit, the optical power of the first lens unitis so strong that the total length of the zoom lens system issuccessfully minimized, but simultaneously the inclination of the imageplane toward the over side becomes unduly large. In addition,barrel-shaped distortion becomes unduly large at the wide-angle end.

It is preferable that the zoom lens systems of the embodiments fulfillCondition (2) below.

0.35<φ2/φW<0.75  (2)

where

φ2 represents the optical power of the second lens unit.

Condition (2) defines, in the form of the optical power of the secondlens unit, the condition to be fulfilled to achieve, as in Condition(1), proper correction of aberrations and keep the size of the zoom lenssystem appropriate. If the value of Condition (2) is equal to or lessthan its lower limit, the optical power of the second lens unit is soweak that aberrations can be corrected properly, but simultaneously thetotal length, as well as the diameter of the front-end lens unit, of thezoom lens system becomes unduly large. In contrast, if the value ofCondition (2) is equal to or greater than its upper limit, the opticalpower of the second lens unit is so strong that the total length of thezoom lens system is successfully minimized, but simultaneously sphericalaberration appears notably on the under side.

It is preferable that the zoom lens systems of the embodiments fulfillCondition (3) below.

−1.2<φPi/φW×hi<1.2  (3)

where

φPi represents the optical power of the ith plastic lens element; and

hi represents the height of incidence at which a paraxial ray enters theobject-side surface of the ith plastic lens element at the telephotoend, assuming that the initial values of the converted inclination α1and the height h1, for paraxial tracing, are 0 and 1, respectively.

Condition (3) defines, in the form of the sum of the degrees in whichthe individual plastic lens elements, by their temperature variation,affect the back focal distance, the condition to be fulfilled tosuppress variation in the back focal distance resulting from temperaturevariation. When a plurality of plastic lens elements are used, it ispreferable that positively-powered and negatively-powered lens elementsbe combined in such a way that the degree in which they affect the backfocal distance are canceled out by one another. If the value ofCondition (3) is equal to or less than its lower limit, the variation inthe back focal distance caused by temperature variation in thenegatively-powered plastic lens element becomes unduly great. Incontrast, if the value of Condition (3) is equal to or greater than itsupper limit, the variation in the back focal distance caused bytemperature variation in the positively-powered plastic lens elementbecomes unduly great. Thus, in either case, the zoom lens system needsto be provided with a mechanism that corrects the back focal distance inaccordance with temperature variation.

It is preferable that the zoom lens systems of the embodiments fulfillCondition (4) below.

|φP/φ1|<1.35  (4)

where

φP represents the optical power of the plastic lens element.

Condition (4) defines, in the form of the optical power of the plasticlens element included in the first lens unit, the condition to befulfilled to keep the variation of aberrations resulting fromtemperature variation within an appropriate range. If the value ofCondition (4) is equal to or greater than its upper limit, curvature offield, in particular, the curvature of field on the wide-angle sidevaries too greatly with temperature.

It is preferable that the zoom lens systems of the embodiments fulfillCondition (5) below.

|φP/φ2|<2.15  (5)

Condition (5) defines, in the form of the optical power of the plasticlens element included in the second lens unit, the condition to befulfilled to keep, as in Condition (4), the variation of aberrationsresulting from temperature variation within an appropriate range. If thevalue of Condition (5) is equal to or greater than its upper limit,spherical aberration, in particular, the spherical aberration on thetelephoto side, varies too greatly with temperature.

No lower limit is given for Conditions (4) and (5). This is because, asthe value of either of the conditions decreases, the optical power ofthe plastic lens element becomes weaker, and this is desirable in termsof suppression of the variation of aberrations resulting fromtemperature variation. This, however, has no effect on correction ofaberrations under normal temperature, and accordingly makes the use ofplastic lenses meaningless. To avoid this, where the plastic lenselement fulfills Condition (6) below, it is essential to use anaspherical surface.

0≦|φP/φA|<0.45  (6)

where

φA represents the optical power of the lens unit including the plasticlens element.

Note however that this is not to discourage providing an asphericalsurface on the lens surface of a plastic lens element having an opticalpower that makes the value of Condition (6) equal to or greater than itsupper limit.

As described above, if an aspherical surface is used, it is preferablethat the following conditions be fulfilled. First, where an asphericalsurface is used in the first lens unit, it is preferable that Condition(7) below be fulfilled.

−0.85<(|X|−|X ₀|)/{C ₀(N′−N)f1}<−0.05  (7)

where

C₀ represents the curvature of the reference spherical surface of theaspherical surface;

N represents the refractive index of the image-side medium of theaspherical surface for the d line;

N′ represents the refractive index of the object-side medium of theaspherical surface for the d line;

X represents the deviation of the aspherical surface along the opticalaxis at the height in a direction perpendicular to the optical axis (thedirection pointing to the object side is negative);

X₀ represents the deviation of the reference spherical surface of theaspherical surface along the optical axis at the height in a directionperpendicular to the optical axis (the direction pointing to the objectside is negative); and

f1 represents the focal length of the first lens unit.

Condition (7) defines the surface shape of the aspherical surface andassumes that the aspherical surface is so shaped as to weaken theoptical power of the first lens unit. Fulfillment of Condition (7) makesit possible to achieve proper correction of the distortion and the imageplane on the wide-angle side, in particular. If the value of Condition(7) is equal to or less than its lower limit, positive distortionbecomes unduly large on the wide-angle side, in particular, in aclose-shooting condition, and simultaneously the inclination of theimage plane toward the over side becomes unduly large. In contrast, ifthe value of Condition (7) is equal to or greater than its upper limit,negative distortion becomes unduly large on the wide-angle side, inparticular, in a close-shooting condition, and simultaneously theinclination of the image plane toward the under side becomes undulylarge. Note that, in a case where the first lens unit includes aplurality of aspherical surfaces, at least one of those asphericalsurfaces needs to fulfill Condition (7) above; that is, the otheraspherical surfaces do not necessarily have to fulfill Condition (7)above, if that is advantageous for the correction of other aberrations.

In a case where an aspherical surface is used in the second lens unit,it is preferable that Condition (8) below be fulfilled.

−0.95<(|X|−|X ₀|)/{C ₀(N′−N)f2}<−0.05  (8)

where

f2 represents the focal length of the second lens unit.

Condition (8) defines the surface shape of the aspherical surface andassumes that the aspherical surface is so shaped as to weaken theoptical power of the second lens unit. Fulfillment of Condition (8)makes it possible to achieve proper correction of spherical aberration,in particular. If the value of Condition (8) is equal to or less thanits lower limit, in particular, spherical aberration appears notably onthe over side at the telephoto end. In contrast, if the value ofCondition (8) is equal to or greater than its upper limit, sphericalaberration appears notably on the under side at the telephoto end. Notethat, in a case where the second lens unit includes a plurality ofaspherical surfaces, at least one of those aspherical surfaces needs tofulfill Condition (8) above; that is, the other aspherical surfaces donot necessarily have to fulfill Condition (8) above, if that isadvantageous for the correction of other aberrations.

Embodiments 6 to 15

FIGS. 11 to 19 and 29 are lens arrangement diagrams of the zoom lenssystems of a sixth, a seventh, an eighth, a ninth, a tenth, an eleventh,a twelfth, a thirteenth, a fourteenth and a fifteenth embodiment,respectively. In each diagram, the left-hand side corresponds to theobject side, and the right-hand side corresponds to the image side. Inaddition, in each diagram, arrows schematically indicate the movement ofthe lens units during zooming from the wide-angle end to the telephotoend. Note that arrows with a broken line indicate that the lens unit iskept in a fixed position during zooming. Moreover, each diagram showsthe lens arrangement of the zoom lens system during zooming, as observedat the wide-angle end. As shown in these diagrams, the zoom lens systemsof the embodiments are each built as a three-unit zoom lens system of anegative-positive- positive configuration that is composed of, from theobject side, a first lens unit Gr1, a second lens unit Gr2, and a thirdlens unit Gr3. In this zoom lens system, at least two lens units aremoved during zooming.

The first lens unit Gr1 has a negative optical power as a whole. Thesecond and third lens units (Gr2 and Gr3) have a positive optical poweras a whole. In the zoom lens system, the first to eighth lens elementscounted from the object side are represented as G1 to G8, respectively.The lens units provided in the zoom lens system of each embodiment areeach realized by the use of a plurality of lens elements out of thoselens elements G1 to G8. The second lens unit Gr2 includes an aperturestop S. Note that a flat plate disposed at the image- side end of thezoom lens system is a low-pass filter LPF.

As shown in FIG. 11, in the sixth embodiment, the second and sixth lenselements (G2 and G6) counted from the object side (hatched in thefigure) are plastic lens elements. Moreover, as shown in FIG. 12, in theseventh embodiment, the second and seventh lens elements (G2 and G7)counted from the object side (hatched in the figure) are plastic lenselements.

As shown in FIG. 13, in the eighth embodiment, the first and seventhlens elements (G1 and G7) counted from the object side (hatched in thefigure) are plastic lens elements. Moreover, as shown in FIG. 14, in theninth embodiment, the second and fifth lens elements (G2 and G5) countedfrom the object side (hatched in the figure) are plastic lens elements.Furthermore, as shown in FIG. 15, in the tenth embodiment, the first andseventh lens elements (G1 and G7) counted from the object side (hatchedin the figure) are plastic lens elements.

As shown in FIG. 16, in the eleventh embodiment, the second and fifthlens elements (G2 and G5) counted from the object side (hatched in thefigure) are plastic lens elements. Moreover, as shown in FIG. 17, in thetwelfth embodiment, the second, fifth, sixth, and seventh lens elements(G2, G5, G6, and G7) counted from the object side (hatched in thefigure) are plastic lens elements.

As shown in FIG. 18, in the thirteenth embodiment, the second, fifth,sixth, seventh, and eighth lens elements (G2, G5, G6, G7, and G8)counted from the object side (hatched in the figure) are plastic lenselements. As shown in FIG. 19, in the fourteenth embodiment, the second,sixth, and seventh lens elements (G2, G6, and G7) counted from theobject side (hatched in the figure) are plastic lens elements. Referringto FIG. 29, in the fifteenth embodiment, the first and fifth lenselements (G1 and G5) are plastic lens elements.

The conditions to be preferably fulfilled by an optical system will bedescribed below. It is preferable that the zoom lens systems of thesixth to fifteenth embodiments fulfill Condition (9) below.

 −0.8<Cp×(N′−N)/φW<0.8  (9)

where

Cp represents the curvature of the plastic lens element;

φW represents the optical power of the entire zoom lens system at thewide-angle end;

N′ represents the refractive index of the object-side medium of theaspherical surface for the d line; and

N represents the refractive index of the image-side medium of theaspherical surface for the d line.

Condition (9) defines the optical power of the lens surface of theplastic lens element. If the optical power of the lens surface is toostrong, the surface shape varies with temperature, with the result thatvarious aberrations become unduly large. If the value of Condition (9)is equal to or less than its lower limit, the negative optical power istoo strong. In contrast, if the value of Condition (9) is equal to orgreater than its upper limit, the positive optical power is too strong.As a result, in the plastic lens element provided in the first lensunit, curvature of field varies too greatly with temperature, inparticular; in the plastic lens element provided in the second lensunit, spherical aberration varies too greatly with temperature, inparticular; and, in the plastic lens element provided in the third lensunit, spherical aberration and the coma aberration in marginal rays varygreatly with temperature, in particular.

It is preferable that the zoom lens systems of the embodiments fulfillCondition (10) below.

−0.45<M3/M2<0.90  (10)

where

M3 represents the amount of movement of the third lens unit (thedirection pointing to the object side is negative with respect to thewide-angle end); and

M2 represents the amount of movement of the second lens unit (thedirection pointing to the object side is negative with respect to thewide-angle end).

Condition (10) defines, in the form of the ratio of the amount ofmovement of the second lens unit to that of the third lens unit, thecondition to be fulfilled to keep the amount of movement of the secondand third lens units in appropriate ranges in order to achieve zoomingefficiently. Thus, in an optical system in which a sufficient zoom rationeeds to be secured, fulfillment of Condition (10) is effective.Moreover, it is more preferable that the following condition beadditionally fulfilled.

φT/φW>1.6

where

φT represents the optical power of the entire zoom lens system at thetelephoto end.

If the value of Condition (10) is equal to or less than its lower limit,the responsibility of the third lens unit for zooming is so heavy thatspherical aberration and the coma aberration in marginal rays vary toogreatly with zooming. In contrast, if the value of Condition (10) isequal to or greater than its upper limit, the amount of the movement ofthe second lens unit is so large that the diameter of the front-end lensunit needs to be unduly large in order to secure sufficient amount ofperipheral light on the wide-angle side, and simultaneously, theresponsibility of the second lens unit for zooming is so heavy thatspherical aberration varies too greatly with zooming.

Moreover, where a plastic lens element is used in the third lens unit,the ability of the third lens unit to correct aberrations tends to beinsufficient. To avoid this, it is preferable to make the range ofCondition (10) narrower so as to obtain the following condition:

−0.30<M3/M2<0.90  (10)

In a case where a plastic lens element is used in the first lens unit,it is preferable that Condition (11) below be fulfilled.

|φP/φ1|<1.20  (11)

where

φP represents the optical power of the plastic lens element; and

φ1 represents the optical power of the first lens unit.

Condition (11) defines, in the form of the ratio of the optical power ofthe first lens unit to that of the plastic lens element included in thefirst lens unit, the condition to be fulfilled to keep the variation ofaberrations resulting from temperature variation within an appropriaterange. If the value of Condition (11) is equal to or greater than itsupper limit, curvature of field, in particular, the curvature of fieldon the wide-angle side, varies too greatly with temperature. Moreover,to correct the aberrations that occur in the first lens unit, it ispreferable to use at least a positive and a negative lens element.

In a case where a plastic lens element is used in the second lens unit,it is preferable that Condition (12) below be fulfilled.

|φP/φ2|<2.5  (12)

where

φ2 represents the optical power of the second lens unit.

Condition (12) defines, in the form of the ratio of the optical power ofthe second lens unit to that of the plastic lens element included in thesecond lens unit, the condition to be fulfilled to keep the variation ofaberrations resulting from temperature variation within an appropriaterange. If the value of Condition (12) is equal to or greater than itsupper limit, spherical aberration, in particular, the sphericalaberration on the telephoto side, varies too greatly with temperature.Moreover, to correct the aberrations that occur in the second lens unit,it is preferable to use at least a positive and a negative lens element.

In a case where a plastic lens element is used in the third lens unit,it is preferable that Condition (13) below be fulfilled.

 |φP/φ3|<1.70  (13)

where

φ3 represents the optical power of the third lens unit.

Condition (13) defines, in the form of the ratio of the optical power ofthe third lens unit to that of the plastic lens element included in thethird lens unit, the condition to be fulfilled to keep the variation ofaberrations resulting from temperature variation within an appropriaterange. If the value of Condition (13) is equal to or greater than itsupper limit, spherical aberration and the coma aberration in marginalrays vary too greatly with temperature. Moreover, to correct theaberrations that occur in the third lens unit, it is preferable to useat least a positive and a negative lens element.

No lower limit is given for Conditions (11) to (13). This is because, asthe value of either of the conditions decreases, the optical power ofthe plastic lens element becomes weaker, and this is desirable in termsof suppression of the variation of aberrations resulting fromtemperature variation. This, however, has no effect on correction ofaberrations under normal temperature, and accordingly makes the use ofplastic lenses meaningless. To avoid this, where the plastic lenselement fulfills Condition (14) below, it is essential to use anaspherical surface.

 0≦|φP/φA|<0.45  (14)

where

φA represents the optical power of the lens unit including the plasticlens element.

Note however that this is not to discourage providing an asphericalsurface on the lens surface of a plastic lens element having an opticalpower that makes the value of Condition (14) equal to or greater thanits upper limit.

As described above, if an aspherical surface is used, it is preferablethat the following conditions be fulfilled. First, where an asphericalsurface is provided on the lens surface of the plastic lens element ofthe first lens unit, it is preferable that Condition (15) below befulfilled.

−1.10<(|X|−|X ₀|)/{C ₀(N′−N)φ1}<−0.10  (15)

where

C₀ represents the curvature of the reference spherical surface of theaspherical surface;

N represents the refractive index of the image-side medium of theaspherical surface for the d line;

N′ represents the refractive index of the object-side medium of theaspherical surface for the d line;

X represents the deviation of the aspherical surface along the opticalaxis at the height in a direction perpendicular to the optical axis (thedirection pointing to the object side is negative);

X₀ represents the deviation of the reference spherical surface of theaspherical surface along the optical axis at the height in a directionperpendicular to the optical axis (the direction pointing to the objectside is negative); and

f1 represents the focal length of the first lens unit.

If the value of Condition (15) is equal to or less than its lower limit,positive distortion becomes unduly large on the wide-angle side, inparticular, in a close-shooting condition, and simultaneously theinclination of the image plane toward the over side becomes undulylarge. In contrast, if the value of Condition (15) is equal to orgreater than its upper limit, it is impossible to make efficient use ofthe aspherical surface, which makes the use of an aspherical surfacemeaningless. As a result, the negative distortion on the wide-angleside, in particular, in a close-shooting condition, and the inclinationof the image plane toward the under side are undercorrected. Note that,in a case where the first lens unit includes a plurality of asphericalsurfaces, at least one of those aspherical surfaces needs to fulfillCondition (15) above; that is, the other aspherical surfaces do notnecessarily have to fulfill Condition (15) above, if that isadvantageous for the correction of other aberrations.

In a case where an aspherical surface is provided on the lens surface ofthe plastic lens element of the second lens unit, it is preferable thatCondition (16) below be fulfilled.

−0.35<(|X|−|X ₀|)/{C ₀(N′−N)f2}<−0.03  (16)

where

f2 represents the focal length of the second lens unit.

Condition (16) assumes that the aspherical surface is so shaped as toweaken the positive optical power of the second lens unit. Fulfillmentof Condition (16) makes it possible to achieve proper correction ofspherical aberration, in particular. If the value of Condition (16) isequal to or less than its lower limit, in particular, sphericalaberration appears notably on the over side at the telephoto end. Incontrast, if the value of Condition (16) is equal to or greater than itsupper limit, it is impossible to make efficient use of the asphericalsurface, which makes the use of an aspherical surface meaningless. As aresult, spherical aberration is undercorrected on the telephoto side, inparticular. Note that, in a case where the second lens unit includes aplurality of aspherical surfaces, at least one of those asphericalsurfaces needs to fulfill Condition (16) above; that is, the otheraspherical surfaces do not necessarily have to fulfill Condition (16)above, if that is advantageous for the correction of other aberrations.

In a case where an aspherical surface is provided on the lens surface ofthe plastic lens element of the third lens unit, it is preferable thatCondition (17) below be fulfilled.

−0.70<(|X|−|X ₀|)/{C ₀(N′−N)f3}<−0.01  (17)

where

f3 represents the focal length of the third lens unit.

Condition (17) assumes that the aspherical surface is so shaped as toweaken the positive optical power of the third lens unit. Fulfillment ofCondition (17) makes it possible to achieve proper correction ofspherical aberration and the coma aberration in marginal rays. If thevalue of Condition (17) is equal to or less than its lower limit,spherical aberration appears notably on the over side, andsimultaneously the coma aberration in marginal rays becomes undulylarge. In contrast, if the value of Condition (17) is equal to orgreater than its upper limit, it is impossible to make efficient use ofthe aspherical surface, which makes the use of an aspherical surfacemeaningless. As a result, spherical aberration and the coma aberrationin marginal rays are undercorrected. Note that, in a case where thethird lens unit includes a plurality of aspherical surfaces, at leastone of those aspherical surfaces needs to fulfill Condition (17) above;that is, the other aspherical surfaces do not necessarily have tofulfill Condition (17) above, if that is advantageous for the correctionof other aberrations.

It is preferable that the zoom lens systems of the embodiments fulfillCondition (18) below.

0.20<|φ1/φW|<0.70  (18)

Condition (18) defines, in the form of the optical power of the firstlens unit, the condition to be fulfilled to achieve proper correction ofaberrations and keep the size of the zoom lens system appropriate. Ifthe value of Condition (18) is equal to or less than its lower limit,the optical power of the first lens unit is so weak that aberrations canbe corrected properly, but simultaneously the total length, as well asthe diameter of the front-end lens unit, of the zoom lens system becomesunduly large. In contrast, if the value of Condition (18) is equal to orgreater than its upper limit, the optical power of the first lens unitis so strong that aberrations become unduly large, in particular, theinclination of the image plane toward the over side becomes undulylarge, and simultaneously barrel-shaped distortion becomes unduly largeon the wide-angle side. In this case, the use of a plastic lens element,which offers a relatively low refractive index and a strictly restrictedrange of dispersion, makes it difficult to correct aberrations properlyand thus requires more lens elements in the zoom lens system.

It is preferable that the zoom lens systems of the embodiments fulfillCondition (19) below.

0.25<φ2/φW<0.75  (19)

Condition (19) defines, in the form of the optical power of the secondlens unit, the condition to be fulfilled to achieve proper correction ofaberrations and keep the size of the zoom lens system appropriate. Ifthe value of Condition (19) is equal to or less than its lower limit,the optical power of the second lens unit is so weak that aberrationscan be corrected properly, but simultaneously the total length, as wellas the diameter of the front-end lens unit, of the zoom lens systembecomes unduly large. In contrast, if the value of Condition (19) isequal to or greater than its upper limit, the optical power of thesecond lens unit is so strong that aberrations become unduly large, inparticular, spherical aberration appears notably on the under side. Inthis case, the use of a plastic lens element, which offers a relativelylow refractive index and a strictly restricted range of dispersion,makes it difficult to correct aberrations properly and thus requiresmore lens elements in the zoom lens system.

It is preferable that the zoom lens systems of the embodiments fulfillCondition (20) below.

0.1<φ3/φW<0.60  (20)

Condition (20) defines, in the form of the optical power of the thirdlens unit, the condition to be fulfilled to achieve proper correction ofaberrations and keep the size of the zoom lens system appropriate. Ifthe value of Condition (20) is equal to or less than its lower limit,the optical power of the third lens unit is so weak that aberrations canbe corrected properly, but simultaneously the total length, as well asthe diameter of the front-end lens unit, of the zoom lens system becomesunduly large. In contrast, if the value of Condition (20) is equal to orgreater than its upper limit, the optical power of the third lens unitis so strong that aberrations become unduly large, in particular,spherical aberration appears notably on the under side. In this case,the use of a plastic lens element, which offers a relatively lowrefractive index and a strictly restricted range of dispersion, makes itdifficult to correct aberrations properly and thus requires more lenselements in the zoom lens system.

Moreover, if the values of Conditions (18) to (20) are equal to orgreater than their upper limits, the optical power of the plastic lenselement tends to be unduly strong. Thus, it is preferable thatConditions (11) and (18); (12) and (19); and (13) and (20) be fulfilledat the same time, respectively.

It is preferable that the zoom lens systems of the embodiments fulfillCondition (21) below.

−1.4<φPi/φW×hi<1.4  (21)

where

φPi represents the optical power of the ith plastic lens element; and

hi represents the height of incidence at which a paraxial ray enters theobject-side surface of the ith plastic lens element at the telephotoend, assuming that the initial values of the converted inclination α1and the height h1, for paraxial tracing, are 0 and 1, respectively.

Condition (21) defines, in the form of the sum of the degrees in whichthe individual plastic lens elements, by their temperature variation,affect the back focal distance, the condition to be fulfilled tosuppress variation in the back focal distance resulting from temperaturevariation. When a plurality of plastic lens elements are used, it ispreferable that positively-powered and negatively-powered lens elementsbe combined in such a way that the degree in which they affect the backfocal distance are canceled out by one another. If the value ofCondition (21) is equal to or less than its lower limit, the variationin the back focal distance caused by temperature variation in thenegatively-powered plastic lens element becomes unduly great. Incontrast, if the value of Condition (21) is equal to or greater than itsupper limit, the variation in the back focal distance caused bytemperature variation in the positively-powered plastic lens elementbecomes unduly great. Thus, in either case, the zoom lens system needsto be provided with a mechanism that corrects the back focal distance inaccordance with temperature variation.

It is preferable that the zoom lens systems of the embodiments fulfillCondition (22) below.

0.5<log(β2T/β2W)/logZ<2.2  (22)

where

β2W represents the lateral magnification of the second lens unit at thewide-angle end;

β2T represents the lateral magnification of the second lens unit at thetelephoto end;

Z represents the zoom ratio; and

log represents a natural logarithm (since the condition defines aproportion, the base does not matter).

In a zoom lens system of the types like those of the present invention,the responsibility of the second lens unit for zooming is heavier thanthat of any other lens unit. The heavier the responsibility for zooming,the larger the aberrations that accompany zooming. Thus, in order toachieve proper correction of aberrations, it is preferable to distributethe responsibility for zooming among a plurality of lens units.Condition (22) defines the responsibility for zooming of the second lensunit, to which the heaviest responsibility for zooming is distributed ina zoom lens system of the types like those of the present invention.

If the value of Condition (22) is equal to or less than its lower limit,the responsibility of the second lens unit for zooming is so light thatthe aberrations occurring in the second lens unit can be correctedproperly. This, however, affects the responsibility of the other lensunits for correcting aberrations, and thus requires more lens elementsin those other lens units, with the result that the entire opticalsystem needs to have an unduly large size. In contrast, if the value ofCondition (22) is equal to or greater than its upper limit, theresponsibility of the second lens unit for zooming is so heavy thatspherical aberration varies too greatly with zooming, in particular.

It is preferable that the zoom lens systems of the embodiments fulfillCondition (23) below.

−1.2<log(β3T/β3W)/logZ<0.5  (23)

where

β3W represents the lateral magnification of the third lens unit at thewide-angle end; and

β3T represents the lateral magnification of the third lens unit at thetelephoto end.

Condition (23) defines the responsibility of the third lens unit forzooming. If the value of Condition (23) is negative, the third lens unitreduces its magnification during zooming. This is disadvantageous fromthe viewpoint of zooming. In this case, however, by moving the thirdlens unit during zooming, it is possible to correct the aberrationsoccurring in the other lens units during zooming. If the value ofCondition (23) is equal to or less than its lower limit, the third lensunit reduces its magnification at an unduly high rate during zooming,and thus the resulting loss in magnification needs to be compensated bythe other lens units. This requires an unduly large number of lenselements in those other lens units and thus makes the entire opticalsystem unduly long. In contrast, if the value of Condition (23) is equalto or greater than its upper limit, the responsibility of the third lensunit for zooming is so heavy that spherical aberration and comaaberration vary too greatly with zooming.

Moreover, it is preferable that the zoom lens systems of the embodimentsfulfill Condition (24) below.

 −0.75<log(β3T/β3W)/log(β2T/β2W)<0.65  (24)

Condition (24) defines the preferable ratio of the responsibility of thesecond lens unit for zooming to the responsibility of the third lensunit for zooming. If the value of Condition (24) is equal to or lessthan its lower limit, the third lens unit reduces its magnification, andthus the responsibility of the second lens unit for zooming isexcessively heavy. As a result, spherical aberration varies too greatlywith zooming. In contrast, if the value of Condition (24) is equal to orgreater than its upper limit, the responsibility of the third lens unitfor zooming is so heavy that spherical aberration and coma aberrationvary too greatly with zooming.

Hereinafter, examples of zoom lens systems embodying the presentinvention will be presented with reference to their construction data,graphic representations of aberrations, and other data. Tables 1 to 5list the construction data of Examples 1 to 5, which respectivelycorrespond to the first to fifth embodiments described above and havelens arrangements as shown in FIGS. 1 to 5. Tables 6 to 15 list theconstruction data of Examples 6 to 15, which respectively correspond tothe sixth to fifteenth embodiments described above and have lensarrangements as shown in FIGS. 11 to 19 and 29.

In the construction data of each example, ri (i=1, 2, 3, . . . )represents the ith surface counted from the object side and its radiusof curvature, di (i=1, 2, 3, . . . ) represents the ith axial distancecounted from the object side, and Ni (i=1, 2, 3, . . . ) and ni (i=1, 2,3, . . . ) respectively represent the refractive index for the d lineand the Abbe number of the ith lens element counted from the objectside. The values listed for the focal length f and the F number FNO ofthe entire zoom lens system in Examples 1 to 5; the distance between thefirst and second lens units; and the distance between the second lensunit and the low-pass filter LPF are the values at, from left, thewide-angle end (W), the middle-focal-length position (M), and thetelephoto end (T).

Moreover, the values listed for the focal length f and the F number FNOof the entire zoom lens system in Examples 6 to 15; the distance betweenthe first and second lens units; the distance between the second andthird lens units; and the distance between the third lens unit and thelow-pass filter LPF are the values at, from left, the wide-angle end(W), the middle-focal-length position (M), and the telephoto end (T).Note that, in all of Examples, a surface whose radius of curvature ri ismarked with an asterisk (*) is an aspherical surface, whose surfaceshape is defined by the following formulae.

X=X ₀ +ΣSA _(i) Y ^(i)  (a)

X ₀ =CY ²/{1+(1−εC ² Y ²)^(½})  (b)

where

X represents the displacement from the reference surface in the opticalaxis direction;

Y represents the height in a direction perpendicular to the opticalaxis;

C represents the paraxial curvature;

ε represents the quadric surface parameter; and

A_(i) represents the aspherical coefficient of the ith order.

FIGS. 6A to 6I, 7A to 7I, 8A to 8I, 9A to 9I, and 10A to 10I show theaberrations observed in the infinite-distance shooting condition inExamples 1 to 5, respectively. Of these diagrams, FIGS. 6A to 6C, 7A to7C, 8A to 8C, 9A to 9C, and 10A to 10C show the aberrations observed atthe wide-angle end [W]; FIGS. 6D to 6F, 7D to 7F, 8D to 8F, 9D to 9F,and 10D to 10F show the aberrations observed at the middle focal length[M]; and FIGS. 6G to 6I, 7G to 7I, 8G to 8I, 9G to 9I, and 10G to 10Ishow the aberrations observed at the telephoto end [T]. In the sphericalaberration diagrams, the solid line (d) represents the d line and thebroken line (SC) represents the sine condition. In the astigmatismdiagrams, the solid line (DS) and the broken line (DM) represent theastigmatism on the sagittal plane and on the meridional plane,respectively. In Examples 1 to 5, Conditions (1) to (5) mentioned aboveare fulfilled.

FIGS. 20A to 20I, 21A to 21I, 22A to 22I, 23A to 23I, 24A to 24I, 25A to25I, 26A to 26I, 27A to 27I, 28A to 28I, and 30A to 30I show theaberrations observed in the infinite-distance shooting condition inExamples 6 to 15, respectively. Of these diagrams, FIGS. 20A to 20C, 21Ato 21C, 22A to 22C, 23A to 23C, 24A to 24C, 25A to 25C, 26A to 26C, 27Ato 27C, 28A to 28C, and 30A to 30C show the aberrations observed at thewide-angle end [W]; FIGS. 20D to 20F, 21D to 21F, 22D to 22F, 23D to23F, 24D to 24F, 25D to 25F, 26D to 26F, 27D to 27F, 28D to 28F, and 30Dand 30F show the aberrations observed at the middle focal length [M];and FIGS. 20G to 20I, 21G to 21I, 22G to 22I, 23G to 23I, 24G to 24I,25G to 25I, 26G to 26I, 27G to 27I, 28G to 28I, and 30G to 30I show theaberrations observed at the telephoto end [T]. In the sphericalaberration diagrams, the solid line (d) represents the d line and thebroken line (SC) represents the sine condition. In the astigmatismdiagrams, the solid line (DS) and the broken line (DM) represent theastigmatism on the sagittal plane and on the meridional plane,respectively. In Examples 6 to 15, the conditions mentioned above arefulfilled.

The variables used in Conditions (1) to (5) in Examples 1 to 5 arelisted in Table 16.

The values corresponding to Conditions (1) to (5) in Examples 1 to 5 arelisted in Table 17.

The values corresponding to Conditions (9) to (13) and (18) to (24) inExamples 6 to 15 are listed in Table 18.

The values corresponding to Conditions (7) and (8) to be fulfilled bythe aspherical surface in Examples 1 to 5 are listed in Table 19. Notethat Y represents the maximum height of the optical path on theaspherical surface.

The values corresponding to Conditions (15) to (17) to be fulfilled bythe aspherical surface in Examples 6 to 15 are listed in Table 20. Notethat Y represents the maximum height of the optical path on theaspherical surface.

TABLE 1 Construction Data of Example 1 f = 5.4 mm 7.5 mm 10.5 mm (FocalLength of the Entire Optical System) FNO = 2.96 mm 3.24 mm 3.6 mm (Fnumbers) Radius of Axial Refractive Abbe Curvature Distance Index (Nd)Number (d) r1 = 11.333  d1 = 0.779 N1 = 1.85000 ν1 = 40.04 r2 = 6.007 d2 = 1.940 r3* = 17.418  d3 = 1.400 N2 = 1.52510 ν2 = 56.38 r4 = 6.396 d4 = 1.895 r5 = 7.432  d5 = 1.763 N3 = 1.84666 ν3 = 23.82 r6 = 10.246 d6 = 13.009 6.374 1.500 r7 = ∞(Aperture Stop)  d7 = 1.500 r8 = 5.989 d8 = 1.829 N4 = 1.75450 ν4 = 51.57 r9 = −125.715  d9 = 1.268 r10 =−12.153 d10 = 0.635 N5 = 1.75000 ν5 = 25.14 r11 = 9.023 d11 = 0.447 r12*= 13.010 d12 = 2.293 N6 = 1.52510 ν6 = 56.38 r13 = −6.778 d13 = 1.0002.559 4.786 r14 = ∞ d14 = 3.400 N7 = 1.54426 ν7 = 69.60 r15 = ∞[Aspherical Coefficients of 3rd Surface (r3)] ε = 0.10000 × 10 A4 =0.21447 × 10⁻³ A6 = 0.50169 × 10⁻⁵ A8 = 0.14584 × 10⁻⁶ [AsphericalCoefficients of 12th Surface (r12)] ε = 0.10000 × 10 A4 = −0.20572 ×10⁻² A6 = −0.42994 × 10⁻⁵ A8 = −0.32617 × 10⁻⁵

TABLE 2 Construction Data of Example 2 f = 5.4 mm 7.5 mm 10.5 mm (FocalLength of the Entire Optical System) FNO = 2.96 mm 3.24 mm 3.6 mm (Fnumbers) Radius of Axial Refractive Abbe Curvature Distance Index (Nd)Number (d) r1 = 14.260  d1 = 0.650 N1 = 1.53359 ν1 = 64.66 r2 = 6.334 d2 = 2.341 r3* = 24.115  d3 = 1.400 N2 = 1.52510 ν2 = 56.38 r4 = 5.871 d4 = 1.561 r5 = 6.894  d5 = 2.091 N3 = 1.58340 ν3 = 30.23 r6 = 13.124 d6 = 14.102 6.837 1.500 r7 = ∞(Aperture Stop)  d7 = 1.500 r8 = 5.164 d8 = 2.262 N4 = 1.61555 ν4 = 57.97 r9 = −9.593  d9 = 0.479 r10* =−5.666 d10 = 1.472 N5 = 1.58340 ν5 = 30.23 r11 = 9.833 d11 = 0.604 r12*= 22.822 d12 = 1.943 N6 = 1.52510 ν6 = 56.38 r13 = −8.802 d13 = 1.0002.422 4.454 r14 = ∞ d14 = 3.400 N7 = 1.54426 ν7 = 69.60 r15 = ∞[Aspherical Coefficients of 3rd Surface (r3)] ε = 0.10000 × 10 A4 =0.16907 × 10⁻³ A6 = 0.35415 × 10⁻⁵ A8 = 0.80238 × 10⁻⁷ [AsphericalCoefficients of 10th Surface (r10)] ε= 0.10000 × 10 A4 = 0.79103 × 10⁻³A6 = 0.24186 × 10⁻⁴ A8 = 0.30525 × 10⁻⁵ [Aspherical Coefficients of 12thSurface (r12)] ε = 0.10000 × 10 A4 = −0.25573 × 10⁻² A6 = −0.15034 ×10⁻⁵ A8 = −0.18614 × 10⁻⁴

TABLE 3 Construction Data of Example 3 f = 5.4 mm 7.5 mm 10.5 mm (FocalLength of the Entire Optical System) FNO = 2.96 mm 3.24 mm 3.6 mm (Fnumbers) Radius of Axial Refractive Abbe Curvature Distance Index (Nd)Number (d) r1 = 11.551  d1 = 1.213 N1 = 1.75450 ν1 = 51.57 r2 = 6.152 d2 = 2.230 r3* = 21.819  d3 = 1.400 N2 = 1.52510 ν2 = 56.38 r4 = 6.113 d4 = 1.835 r5 = 7.256  d5 = 2.216 N3 = 1.69961 ν3 = 26.60 r6 = 11.287 d6 = 13.126 6.424 1.500 r7 = ∞(Aperture Stop)  d7 = 1.500 r8 = 5.207 d8 = 2.259 N4 = 1.61213 ν4 = 58.19 r9 = −9.240  d9 = 0.467 r10* =−5.774 d10 = 1.430 N5 = 1.58340 ν5 = 30.23 r11 = 9.548 d11 = 0.601 r12*= 22.409 d12 = 1.984 N6 = 1.52510 ν6 = 56.38 r13 = −8.485 d13 = 1.0002.495 4.630 r14 = ∞ d14 = 3.400 N7 = 1.54426 ν7 = 69.60 r15 = ∞[Aspherical Coefficients of 3rd Surface (r3)] ε = 0.10000 × 10 A4 =0.19262 × 10⁻³ A6 = 0.34894 × 10⁻⁵ A8 = 0.12515 × 10⁻⁶ [AsphericalCoefficients of 10th Surface (r10)] ε = 0.10000 × 10 A4 = 0.43913 × 10⁻³A6 = 0.33312 × 10⁻⁴ A8 = 0.24577 × 10⁻⁵ [Aspherical Coefficients of 12thSurface (r12)] ε = 0.10000 × 10 A4 = −0.22305 × 10⁻² A6 = −0.11486 ×10⁻⁴ A8 = −0.15332 × 10⁻⁴

TABLE 4 Construction Data of Example 4 f = 5.4 mm 7.5 mm 10.5 mm (FocalLength of the Entire Optical System) FNO= 2.9 mm 3.25 mm 3.6 mm (Fnumbers) Radius of Axial Refractive Abbe Curvature Distance Index (Nd)Number (d) r1 = 13.912  d1 = 1.500 N1 = 1.75450 ν1 = 51.57 r2 = 6.626 d2 = 2.111 r3 = 25.350  d3 = 1.000 N2 = 1.75450 ν2 = 51.57 r4 = 7.001 d4 = 0.893 r5* = 14.283  d5 = 4.843 N3 = 1.58340 ν3 = 30.23 r6* =−45.283  d6 = 15.765 7.542 1.500 r7 = ∞(Aperture Stop)  d7 = 1.500 r8 =5.964  d8 = 4.216 N4 = 1.65656 ν4 = 55.63 r9 = −7.373  d9 = 0.208 r10 =−6.131 d10 = 1.300 N5 = 1.58340 ν5 = 30.23 r11* = 9.768 d11 = 2.852 r12= −77.516 d12 = 1.708 N6 = 1.52200 ν6 = 65.93 r13 = −8.818 d13 = 1.0002.668 5.052 r14 = ∞ d14 = 3.400 N7 = 1.54426 ν7 = 69.60 r15 = ∞[Aspherical Coefficients of 5th Surface (r5)] ε = 0.10000 × 10 A4 =0.90348 × 10⁻⁴ A6 = 0.13458 × 10⁻⁵ A8 = 0.14476 × 10⁻⁶ [AsphericalCoefficients of 6th Surface (r6)] ε = 0.10000 × 10 A4 = −0.32219 × 10⁻³A6 = −0.25483 × 10⁻⁵ A8 = −0.86784 × 10⁻⁷ [Aspherical Coefficients of11th Surface (r11)] ε = 0.10000 × 10 A4 = 0.20489 × 10⁻² A6 = 0.27321 ×10⁻⁴ A8 = 0.40971 × 10⁻⁵ A10 = −0.20451 × 10⁻⁶

TABLE 5 Construction Data of Example 5 f = 5.4 mm 7.5 mm 10.5 mm (FocalLength of the Entire Optical System) FNO = 3.18 mm 3.55 mm 4.08 mm (Fnumbers) Radius of Axial Refractive Abbe Curvature Distance Index (Nd)Number (d) r1 = 10.456  d1 = 2.128 N1 = 1.85000 ν1 = 40.04 r2 = 3.870 d2 = 2.166 r3* = 16.226  d3 = 1.400 N2 = 1.52510 ν2 = 56.38 r4 = 6.827 d4 = 1.322 r5 = 8.144  d5 = 1.514 N3 = 1.83350 ν3 = 21.00 r6 = 13.791 d6 = 8.994 4.674 1.500 r7 = ∞(Aperture Stop)  d7 = 1.500 r8 = 5.950  d8= 1.897 N4 = 1.74989 ν4 = 51.73 r9 = −43.969  d9 = 1.242 r10 = −11.144d10 = 0.753 N5 = 1.84714 ν5 = 25.28 r11 = 10.245 d11 = 0.400 r12* =12.590 d12 = 2.297 N6 = 1.52510 ν6 = 56.38 r13 = −6.634 d13 = 1.0003.314 6.620 r14 = ∞ d14 = 3.400 N7 = 1.54426 ν7 = 69.60 r15 = ∞[Aspherical Coefficients of 3rd Surface (r3)] ε = 0.10000 × 10 A4 =0.13045 × 10⁻² A6 = 0.11643 × 10⁻⁴ A8 = 0.51406 × 10⁻⁵ [AsphericalCoefficients of 12th Surface (r12)] ε = 0.10000 × 10 A4 = −0.22747 ×10⁻² A6 = −0.36716 × 10⁻⁵ A8 = −0.32887 × 10⁻⁵

TABLE 6 Construction Data of Example 6 f = 5.4 mm 7.5 mm 10.5 mm (FocalLength of the Entire Optical System) FNO = 2.74 3.11 3.60 (F numbers)Radius of Axial Refractive Abbe Curvature Distance Index (Nd) Number (d)r1 = 13.380  d1 = 0.650 N1 = 1.75450 ν1 = 51.57 r2 = 5.890  d2 = 1.499r3* = 12.328  d3 = 1.400 N2 = 1.52510 ν2 = 56.38 r4 = 5.632  d4 = 1.632r5 = 7.068  d5 = 1.753 N3 = 1.84777 ν3 = 27.54 r6 = 10.246  d6 = 10.4065.264 1.500 r7 = ∞(Aperture Stop)  d7 = 1.500 r8 = 5.643  d8 = 1.901 N4= 1.79073 ν4 = 46.15 r9 = −74.805  d9 = 0.921 r10 = −12.842 d10 = 0.600N5 = 1.72145 ν5 = 25.50 r11 = 5.928 d11 = 0.400 r12* = 11.144 d12 =2.170 N6 = 1.52510 ν6 = 56.38 r13 = −9.099 d13 = 1.000 3.519 7.154 r14 =11.107 d14 = 3.164 N7 = 1.51680 ν7 = 64.20 r15 = 56.703 d15 = 0.796 r16= ∞ d16 = 3.400 N8 = 1.54426 ν8 = 69.60 r17 = ∞ [Aspherical Coefficientsof 3rd Surface (r3)] ε = 0.10000 × 10 A4 = 0.38905 × 10⁻³ A6 = 0.24379 ×10⁻⁵ A8 = 0.38282 × 10⁻⁶ [Aspherical Coefficients of 12th Surface (r12)]ε = 0.10000 × 10 A4 = −0.13386 × 10⁻² A6 = −0.11975 × 10⁻⁴ A8 = −0.53773× 10⁻⁵

TABLE 7 Construction Data of Example 7 f = 5.4 mm 7.5 mm 10.5 mm (FocalLength of the Entire Optical System) FNO = 2.73 3.10 3.60 (F numbers)Radius of Axial Refractive Abbe Curvature Distance Index (Nd) Number (d)r1 = 14.718  d1 = 0.650 N1 = 1.75450 ν1 = 51.57 r2 = 6.639  d2 = 1.307r3* = 11.594  d3 = 1.400 N2 = 1.52510 ν2 = 56.38 r4 = 5.294  d4 = 1.465r5 = 6.937  d5 = 1.858 N3 = 1.84759 ν3 = 26.85 r6 = 10.034  d6 = 10.6215.340 1.500 r7 = ∞(Aperture Stop)  d7 = 1.500 r8 = 6.969  d8 = 2.905 N4= 1.85000 ν4 = 40.04 r9 = −11.743  d9 = 0.210r10 = −8.399 d10 = 1.855 N5= 1.72131 ν5 = 25.51 r11 = 5.522 d11 = 0.400 r12 = 11.032 d12 = 2.012 N6= 1.75450 ν6 = 51.57 r13= −21.657 d13 = 1.000 3.398 6.919 r14* = 8.536d14 = 3.241 N7 = 1.52510 ν7 = 56.38 r15 = 29.006 d15 = 0.676 r16 = ∞ d16= 3.400 N8 = 1.54426 ν8 = 69.60 r17 = ∞ [Aspherical Coefficients of 3rdSurface (r3)] ε = 0.10000 × 10 A4 = 0.35342 × 10⁻³ A6 = 0.71258 × 10⁻⁶A8 = 0.33647 × 10⁻⁶ [Aspherical Coefficients of 14th Surface (r14)] ε =0.10000 × 10 A4 = −0.23473 × 10⁻³ A6 = 0.43912 × 10⁻⁵ A8 = 0.10409 ×10⁻⁶

TABLE 8 Construction Data of Example 8 f = 5.4 mm 7.5 mm 10.5 mm (FocalLength of the Entire Optical System) FNO = 2.75 3.10 3.60 (F numbers)Radius of Axial Refractive Abbe Curvature Distance Index (Nd) Number (d)r1* = 14.652  d1 = 1.200 N1 = 1.58340 ν1 = 30.23 r2 = 8.289  d2 = 1.623r3 = 26.068  d3 = 0.900 N2 = 1.79271 ν2 = 45.90 r4 = 5.496  d4 = 1.179r5 = 7.356  d5 = 1.921 N3 = 1.84666 ν3 = 23.82 r6 = 15.373  d6 = 10.2245.176 1.500 r7 = ∞(Aperture Stop)  d7 = 1.500 r8 = 7.124  d8 = 3.411 N4= 1.85000 ν4 = 40.04 r9 = −11.538  d9 = 0.154 r10 = −8.339 d10 = 1.713N5 = 1.72418 ν5 = 25.37 r11 = 5.686 d11 = 0.401 r12 = 10.731 d12 = 2.078N6 = 1.75450 ν6 = 51.57 r13 = −18.326 d13 = 1.000 3.307 6.708 r14* =8.148 d14 = 3.002 N7 = 1.52510 ν7 = 56.38 r15 = 16.995 d15 = 0.795 r16 =∞ d16 = 3.400 N8 = 1.54426 ν8 = 69.60 r17 = ∞ [Aspherical Coefficientsof 1st Surface (r1)] ε = 0.10000 × 10 A4 = 0.15951 × 10⁻³ A6 = 0.14779 ×10⁻⁶ A8 = 0.56026 × 10⁻⁷ [Aspherical Coefficients of 14th Surface (r14)]ε = 0.10000 × 10 A4 = −0.27776 × 10⁻³ A6 = 0.23365 × 10⁻⁵ A8 = 0.19731 ×10⁻⁶

TABLE 9 Construction Data of Example 9 f = 5.4 mm 7.5 mm 10.5 mm (FocalLength of the Entire Optical System) FNO = 2.73 3.10 3.60 (F numbers)Radius of Axial Refractive Abbe Curvature Distance Index (Nd) Number (d)r1 = 52.355 d1 = 1.100 N1 = 1.72677 ν1 = 52.55 r2 = 6.927 d2 = 3.324 r3*= 23.902 d3 = 1.940 N2 = 1.58340 ν2 = 30.23 r4 = −100.448 d4 = 14.8277.138 1.500 r5 = ∞(Aperture Stop) d5 = 1.500 r6 = 5.036 d6 = 3.339 N3 =1.77742 ν3 = 47.95 r7 = −12.586 d7 = 0.234 r8 = −10.396 d8 = 0.800 N4 =1.79850 ν4 = 22.60 r9 = 16.524 d9 = 0.740 r10 = −7.142 d10 = 1.200 N5 =1.58340 ν5 = 30.23 r11* = −26.834 d11 = 1.000 2.921 5.663 r12 = 15.086d12 = 2.096 N6 = 1.48749 ν6 = 70.44 r13 = −14.941 d13 = 0.500 r14 = ∞d14 = 3.400 N7 = 1.54426 ν7 = 69.60 r15 = ∞ Aspherical Coefficients of3rd Surface (r3) ε = 0.10000 × 10 A4 = 0.24908 × 10⁻³ A6 = −0.62198 ×10⁻⁷ A8 = 0.10295 × 10⁻⁶ Aspherical Coefficients of 11th Surface (r11) ε= 0.10000 × 10 A4 = 0.39625 × 10⁻² A6 = 0.16585 × 10⁻³ A8 = 0.13563 ×10⁻⁴

TABLE 10 Construction Data of Example 10 f = 5.4 mm 7.5 mm 10.5 mm(Focal Length of the Entire Optical System) FNO = 2.75 3.11 3.60 (Fnumbers) Radius of Axial Refractive Abbe Curvature Distance Index (Nd)Number (d) r1* = 17.928 d1 = 1.200 N1 = 1.58340 ν1 = 30.23 r2 = 9.608 d2= 1.325 r3 = 19.410 d3 = 0.900 N2 = 1.80280 ν2 = 44.68 r4 = 5.204 d4 =1.288 r5 = 7.294 d5 = 1.940 N3 = 1.84666 ν3 = 23.82 r6 = 14.586 d6 =10.102 5.348 1.500 r7 = ∞(Aperture Stop) d7 = 1.500 r8 = 6.594 d8 =4.206 N4 = 1.81063 ν4 = 43.80 r9 = −10.411 d9 = 0.208 r10 = −7.270 d10 =0.600 N5 = 1.70098 ν5 = 26.53 r11 = 5.447 d11 = 0.504 r12 = 10.684 d12 =2.062 N6 = 1.75450 ν6 = 51.57 r13 = −20.769 d13 = 1.000 3.880 6.996 r14*= 6.351 d14 = 2.209 N7 = 1.52510 ν7 = 56.38 r15 = 12.184 d15 = 1.0550.800 1.067 r16 = ∞ d16 = 3.400 N8 = 1.54426 ν8 = 69.60 r17 = ∞Aspherical Coefficients of 1st Surface (r1) ε = 0.10000 × 10 A4 =0.19398 × 10⁻³ A6 = 0.47895 × 10⁻⁶ A8 = 0.46069 × 10⁻⁷ AsphericalCoefficients of 14th Surface (r14) ε = 0.10000 × 10 A4 = −0.37579 × 10⁻³A6 = −0.11089 × 10⁻⁵ A8 = 0.87379 × 10⁻⁷

TABLE 11 Construction Data of Example 11 f = 5.4 mm 7.5 mm 10.5 mm(Focal Length of the Entire Optical System) FNO = 2.97 3.27 3.60 (Fnumbers) Radius of Axial Refractive Abbe Curvature Distance Index (Nd)Number (d) r1 = −112.214 d1 = 1.200 N1 = 1.63347 ν1 = 56.87 r2 = 7.682d2 = 1.473 r3* = 17.799 d3 = 2.175 N2 = 1.58340 ν2 = 30.23 r4 = 274.206d4 = 16.482 8.078 1.500 r5 = ∞(Aperture Stop) d5 = 1.500 r6 = 5.066 d6 =2.164 N3 = 1.84746 ν4 = 40.25 r7 = −15.255 d7 = 0.208 r8 = −13.752 d8 =0.800 N4 = 1.79850 ν5 = 22.60 r9 = 7.640 d9 = 0.352 r10* = 8.419 d10 =1.200 N5 = 1.58340 ν6 = 30.23 r11 = 4.700 d11 = 1.000 1.802 2.808 r12 =40.534 d12 = 2.262 N6 = 1.51838 ν7 = 66.35 r13* = −6.756 d13 = 1.1312.007 3.472 r14 = ∞ d14 = 3.400 N7 = 1.54426 ν8 = 69.60 r15 = ∞Aspherical Coefficients of 3rd Surface (r3) ε = 0.10000 × 10 A4 =0.24372 × 10⁻³ A6 = −0.10309 × 10⁻⁶ A8 = 0.84837 × 10⁻⁷ AsphericalCoefficients of 10th Surface (r10) ε = 0.10000 × 10 A4 = −0.35107 × 10⁻²A6 = −0.17279 × 10⁻³ A8 = −0.80824 × 10⁻⁵ Aspherical Coefficients of13th Surface (r13) ε = 0.10000 × 10 A4 = 0.11613 × 10⁻³ A6 = −0.34635 ×10⁻⁴ A8 = 0.66386 × 10⁻⁶

TABLE 12 Construction Data of Example 12 f = 5.4 mm 8.0 mm 12.0 mm(Focal Length of the Entire Optical System) FNO = 2.55 2.95 3.60 (Fnumbers) Radius of Axial Refractive Abbe Curvature Distance Index (Nd)Number (d) r1 = 64.355 d1 = 0.650 N1 = 1.48749 ν1 = 70.44 r2 = 9.616 d2= 1.136 r3* = 15.072 d3 = 1.400 N2 = 1.52510 ν2 = 56.38 r4 = 6.352 d4 =1.939 r5 = 8.584 d5 = 2.060 N3 = 1.84877 ν3 = 32.01 r6 = 12.547 d6 =15.531 7.207 1.500 r7 = ∞Aperture Stop) d7 = 1.500 r8 = 5.666 d8 = 3.346N4 = 1.75450 ν4 = 51.57 r9 = −8.847 d9 = 0.100 r10 = −7.390 d10 = 0.600N5 = 1.58340 ν5 = 30.23 r11 = 4.818 d11 = 0.400 r12* = 6.048 d12 = 2.459N6 = 1.52510 ν6 = 56.38 r13 = 9.906 d13 = 1.000 3.334 6.995 r14 = 11.941d14 = 1.979 N7 = 1.52510 ν7 = 56.38 r15* = −29.235 d15 = 0.500 r16 = ∞d16 = 3.400 N8 = 1.54426 ν8 = 69.60 r17 = ∞ Aspherical Coefficients of3rd Surface (r3) ε = 0.10000 × 10 A4 = 0.17978 × 10⁻³ A6 = −0.30828 ×10⁻⁶ A8 = 0.71904 × 10⁻⁷ Aspherical Coefficients of 12th Surface (r12) ε= 0.10000 × 10 A4 = −0.18066 × 10⁻² A6 = −0.54257 × 10⁻⁴ A8 = −0.76508 ×10⁻⁵ Aspherical Coefficients of 15th Surface (r15) ε = 0.10000 × 10 A4 =0.29756 × 10⁻³ A6 = −0.62953 × 10⁻⁵ A8 = −0.77785 × 10⁻⁷

TABLE 13 Construction Data of Example 13 f = 5.4 mm 8.8 mm 14.0 mm(Focal Length of the Entire Optical System) FNO = 2.34 2.84 3.60 (Fnumbers) Radius of Axial Refractive Abbe Curvature Distance Index (Nd)Number (d) r1 = 25.623 d1 = 0.650 N1 = 1.48749 ν1 = 70.44 r2 = 9.290 d2= 1.626 r3* = 19.577 d3 = 1.400 N2 = 1.52510 ν2 = 56.38 r4 = 5.973 d4 =2.273 r5 = 7.949 d5 = 2.008 N3 = 1.84807 ν3 = 28.75 r6 = 10.541 d6 =16.801 7.154 1.500 r7 = ∞(Aperture Stop) d7 = 1.500 r8 = 5.107 d8 =2.743 N4 = 1.64626 ν4 = 56.17 r9 = −9.178 d9 = 0.100 r10 = −8.533 d10 =0.600 N5 = 1.58340 ν5 = 30.23 r11 = 7.962 d11 = 0.849 r12* = 7.572 d12 =1.401 N6 = 1.52510 ν6 = 56.38 r13 = 8.290 d13 = 1.000 4.278 9.371 r14* =9.062 d14 = 1.423 N7 = 1.58340 ν7 = 30.23 r15 = 6.924 d15 = 0.747 r16 =11.941 d16 = 1.979 N8 = 1.52510 ν8 = 56.38 r17* = −29.488 d17 = 0.500r18 = ∞ d18 = 3.400 N9 = 1.54426 ν8 = 69.60 r19 = ∞ AsphericalCoefficients of 3rd Surface (r3) ε = 0.10000 × 10 A4 = 0.16055 × 10⁻³ A6= 0.48397 × 10⁻⁷ A8 = 0.67121 × 10⁻⁷ Aspherical Coefficients of 12thSurface (r12) ε = 0.10000 × 10 A4 = −0.25048 × 10⁻² A6 = −0.87701 × 10⁻⁴A8 = −0.12082 × 10⁻⁴ Aspherical Coefficients of 14th Surface (r14) ε =0.10000 × 10 A4 = −0.52484 × 10⁻³ A6 = 0.58442 × 10⁻⁵ A8 = 0.87159 ×10⁻⁸ Aspherical Coefficients of 17th Surface (r17) ε = 0.10000 × 10 A4 =−0.91828 × 10⁻³ A6 = −0.59033 × 10⁻⁵ A8 = 0.27335 × 10⁻⁶

TABLE 14 Construction Data of Example 14 f =5.4 mm  7.5 mm 13.5 mm(Focal Length of the Entire Optical System) FNO =2.08 2.48 3.60 (Fnumbers) Radius of Axial Refractive Abbe Curvature Distance Index (Nd)Number (d) r1 = 14.018 d1 = 0.650 N1 =1.74388 vl = 51.93 r2 = 6.286 d2 =1.790 r3* = 17.191 d3 = 1.400 N2 =1.52510 v2 = 56.38 r4 = 5.770 d4 =0.907 r5 = 6.726 d5 = 1.953 N3 =1.84666 v3 = 23.82 r6 = 10.531 d6 =9.731 5.843 1.500 r7 = ∞(Aperture Stop) d7 = 1.500 r8 = 6.489 d8 = 1.774N4 =1.85000 v4 = 40.04 r9 = 52.968 d9 = 0.665 r10 =−31.304 d10 = 0.600N5 =1.77185 v5 = 23.46 r11 = 6.642 d11 = 0.400 r12* = 11.190 d12 = 2.101N6 =1.52510 v6 = 56.38 r13 = −9.334 d13 = 1.000 5.310 15.247 r14=−10.861 d14 = 1.200 N7 =1.58340 v7 = 30.23 r15* = 16.708 d15 = 0.100r16 = 12.354 d16 = 2.934 N8 =1.84353 v8 = 40.59 r17 =−10.876 d17 = 2.9142.385 0.717 r18 = ∞ d18 = 3.400 N9 =1.54426 v9 = 69.60 r19 = ∞[Aspherica1 Coefficients of 3rd Surface (r3)] ε = 0.10000 × 10 A4 =0.28799 × 10⁻³ A6 = 0.40089 × 10⁻⁵ A8 = 0.14823 × 10⁻⁶ [Aspherica1Coefficients of 12th Surface (r12)] ε = 0.10000 × 10 A4 = −0.62816 ×10⁻³ A6 = −0.22891 × 10⁻⁴ A8 = 0.42945 × 10⁻⁶ [Aspherica1 Coefficientsof 15th Surface (r15)] ε = 0.10000 × 10 A4 = 0.60130 × 10⁻³ A6 =−0.42374× 10⁻⁵ A8 = 0.11268 × 10⁻⁷

TABLE 15 Construction Data of Example 15 f = 5.4 mm 8.4 mm 15.6 mm(Focal Length of the Entire Optical System) FNO = 2.57 3.04 4.20 (Fnumbers) Radius of Axial Refractive Abbe Curvature Distance Index (Nd)Number (d) r1 = 34.564 d1 = 1.600 N1 = 1.52510 ν1 = 56.38 r2 = 7.185 d2= 3.500 r3* = 10.666 d3 = 2.344 N2 = 1.75000 ν2 = 25.14 r4 = 17.516 d4 =22.572 11.179 1.713 r5 = ∞ d5 = 1.500 r6 = 8.000 d6 = 2.941 N3 = 1.80420ν3 = 46.50 r7 = −8.598 d7 = 0.010 N4 = 1.51400 ν4 = 42.83 r8 = −8.598 d8= 0.600 N5 = 1.70055 ν5 = 30.11 r9 = 8.182 d9 = 0.200 r10* = 5.244 d10 =3.249 N6 = 1.52510 ν6 = 56.38 r11* = 6.000 d11 = 2.740 5.844 13.277 r12= 21.195 d12 = 2.000 N7 = 1.48749 ν7 = 70.44 r13 = −16.672 d13 = 1.086r14 = ∞ d14 = 3.400 N8 = 1.51680 ν8 = 64.20 r15 = ∞ AsphericalCoefficients of 3rd Surface (r1) ε = 0.10000 × 10 A4 = 0.43400 × 10⁻³ A6= −0.55461 × 10⁻⁵ A8 = 0.27915 × 10⁻⁷ Aspherical Coefficients of 12thSurface (r2) ε = 0.10000 × 10 A4 = 0.26861 × 10⁻³ A6 = 0.25040 × 10⁻⁵ A8= 0.23353 × 10⁻⁶ Aspherical Coefficients of 15th Surface (r10) ε =0.10000 × 10 A4 = −0.30306 × 10⁻³ A6 = −0.13415 × 10⁻⁴ A8 = −0.19911 ×10⁻⁵ Aspherical Coefficients of 15th Surface (r11 ε = 0.10000 × 10 A4 =0.19342 × 10⁻² A6 = 0.59893 × 10⁻⁴ A8 = −0.42081 × 10⁻⁵

TABLE 16 The variables used in Conditions (1) to (5) in Examples 1 to 5φ1 φ2 φW Example 1 0.076171 0.102604 0.185185 φPi hi φPi/φW × hi SumExample 1 G2: −0.04968 1.088763 −0.292107 G6: 0.11313 1.264821 0.77268210.480575 φ1 φ2 φW Example 2 0.069512 0.102665 0.185162 φPi hi φPi/φW ×hi Sum Example 2 G2: −0.06587 1.090648 −0.387944 G3: 0.045137 1.2995940.3167591 G5: −0.16797 1.270288 −1.152222 G6: 0.080916 1.2079 0.5277862−0.69562 φ1 φ2 φW Example 3 0.07421 0.104252 0.185186 φPi hi φPi/φW × hiSum Example 3 G2: −0.05994 1.070319 −0.346422 G3: −0.16771 1.288669−1.167062 G5: 0.083429 1.23342 0.555676 −0.95781 φ1 φ2 φW Example 40.070779 0.089085 0.185184 φPi hi φPi/φW × hi Sum Example 4 G3: 0.052121.068396 0.3006979 G5: −0.15954 1.348671 −1.161906 −0.86121 φ1 φ2 φWExample 5 0.115 0.104369 0.185185 φPi hi φPi/φW × hi Sum Example 5 G2:−0.04227 1.161585 −0.265113 G6: 0.11589 1.553375 0.9721086 0.706996

TABLE 17 The values corresponding to Conditions (1) to (5) in Examples 1to 5 |φ1/φW| φ2/φW |φP/φ1| |φP/φ2| ΣφPi/φW × hi Example 1 0.41 0.55 G2:0.65 G6: 1.10  0.48 Example 2 0.38 0.55 G2: 0.95 G5: 1.64 −0.70 G3: 0.65G6: 0.79 Example 3 0.40 0.56 G2: 0.81 G5: 1.61 −0.96 G6: 0.80 Example 40.38 0.48 G3: 0.74 G5: 1.79 −0.86 Example 5 0.62 0.56 G2: 0.37 G6: 1.11 0.71

TABLE 18 The values corresponding to Conditions (9) to (13) and (18) to(24) in Examples 6 to 15 |φP/φW| |φP/φ1| |φP/φ2| |φP/φ3| M3/M2 Example 6G2: 0.25 0.63 0.00 G6: 0.55 1.10 Example 7 G2: 0.27 0.72 0.00 G7: 0.251.00 Example 8 G1: 0.15 0.39 0.00 G7: 0.20 1.00 Example 9 G2: 0.16 0.590.00 G5: 0.32 0.68 Example 10 G1: 0.14 0.38 0.00 G7: 0.24 0.47 1.00Example 11 G2: 0.17 0.57 0.56 G5: 0.26 0.65 Example 12 G2: 0.24 0.860.00 G5: 1.10 2.27 G6: 0.22 0.46 G7: 0.33 1.00 Example 13 G2: 0.32 0.970.00 G5: 0.78 1.64 G6: 0.05 0.11 G7: 0.08 0.35 G8: 0.33 1.40 Example 14G2: 0.31271 0.79 −0.18 G6: 0.5375 1.19 G7: 0.48626 1.38log(β2T/β2W)/logZ log(β3T/β3W)/logZ Example 6 G2: 1.00 0.00 Example 7G2: 1.00 0.00 Example 8 G1: 1.00 0.00 Example 9 G2: 0.99 0.01 Example 10G1: 1.00 0.00 Example 11 G2: 1.87 −0.87 Example 12 G2: 0.99 0.01 Example13 G2: 1.00 0.00 Example 14 G2: 0.75 0.25 log(β3T/β3W)/log(β2T/β2W)Example 6 G2: 0.00 Example 7 G2: 0.00 Example 8 G1: 0.00 Example 9 G2:0.01 Example 10 G1: 0.00 Example 11 G2: −0.46 Example 12 G2: 0.01Example 13 G2: 0.00 Example 14 G2: 0.34 φP/φW × h ΣφPi/φW × hi Example 6G2: −0.27 G6: 0.66 0.39 Example 7 G2: −0.28 G7: 0.17 −0.12 Example 8 G1:−0.15 G7: 0.14 −0.01 Example 9 G2: 0.21 G5: −0.30 −0.09 Example 10 G1:−0.14 G7: 0.16 0.02 Example 11 G2: 0.19 G5: −0.26 −0.08 Example 12 G2:−0.26 G5: −1.20 G6: 0.23 G7: 0.16 −1.06 Example 13 G2: −0.33 G5: −0.93G6: 0.06 G7: −0.04 G8: 0.14 −1.10 Example 14 G2: −0.34 G6: 0.68 G7:−0.25 0.09 |φ1/φW| φ2/φW φ3/φW Example 6 G2: 0.40 0.50 0.21 Example 7G2: 0.37 0.50 0.25 Example 8 G1: 0.40 0.52 0.20 Example 9 G2: 0.27 0.470.34 Example 10 G1: 0.38 0.51 0.24 Example 11 G2: 0.29 0.40 0.48 Example12 G2: 0.29 0.48 0.33 Example 13 G2: 0.33 0.47 0.23 Example 14 G2: 0.390.45 0.35 Cp × (N′-N)/φW Object side Image side Example 6 G2: 0.23 −0.50G6: 0.25 0.31 Example 7 G2: 0.25 −0.54 G7: 0.33 −0.10 Example 8 G1: 0.22−0.38 G7: 0.35 −0.17 Example 9 G2: 0.13 0.031 G5: −0.44 0.12 Example 10G1: 0.18 −0.33 G7: 0.45 −0.23 Example 11 G2: 0.18 −0.01 G5: 0.37 −0.67Example 12 G2: 0.19 −0.45 G5: −0.43 −0.65 G6: 0.47 −0.29 G7: 0.24 0.10Example 13 G2: 0.15 −0.48 G5: −0.37 −0.40 G6: 0.37 −0.34 G7: 0.35 −0.46G8: 0.24 0.10 Example 14 G2: 0.17 −0.49 G6: 0.25 0.30 G7: −0.29 −0.19

TABLE 19 The values corresponding to Conditions (7) and (8) in Examples1 to 5 Example 1 [3rd Surface (r3)] Height (|X|−|X0|)/{C0(N′-N) · f1}0.00Y −0.00000 0.20Y −0.00037 0.40Y −0.00634 0.60Y −0.03585 0.80Y−0.13341 1.00Y −0.40394 [12th Surface (r12)] Height (|X|−|X0|)/{C0(N′-N)· f2} 0.00Y −0.00000 0.20Y −0.00037 0.40Y −0.00598 0.60Y −0.03057 0.80Y−0.09885 1.00Y −0.25219 Example 2 [3rd Surface (r3)] Height(|X|−|X0|)/{C0(N′-N) · f1} 0.00Y −0.00000 0.20Y −0.00051 0.40Y −0.008700.60Y −0.04931 0.80Y −0.18376 1.00Y −0.55608 [10th Surface (r10)] Height(|X|−|X0|)/{C0(N′-N) · f2} 0.00Y −0.00000 0.20Y 0.00005 0.40Y 0.000770.60Y 0.00408 0.80Y 0.01399 1.00Y 0.03852 [12th Surface (r12)] Height(|X|−|X0|)/{C0(N′-N) · f2} 0.00Y 0.00000 0.20Y −0.00072 0.40Y −0.011690.60Y −0.06096 0.80Y −0.20787 1.00Y −0.58532 Example 3 [3rd Surface(r3)] Height (|X|−|X0|)/{C0(N′-N) · f1} 0.00Y −0.00000 0.20Y −0.000500.40Y −0.00851 0.60Y −0.04778 0.80Y −0.17765 1.00Y −0.54143 [10thSurface (r10)] Height (|X|−|X0|)/{C0(N′-N) · f2} 0.00Y −0.00000 0.20Y0.00003 0.40Y 0.00046 0.60Y 0.00259 0.80Y 0.00945 1.00Y 0.02790 [12thSurface (r12)] Height (|X|−|X0|)/{C0(N′-N) · f2} 0.00Y 0.00000 0.20Y−0.00065 0.40Y −0.01058 0.60Y −0.05546 0.80Y −0.19007 1.00Y −0.53702Example 4 [5th Surface (r5)] Height (|X|−|X0|)/{Co(N′-N) · f1} 0.00Y−0.00000 0.20Y −0.00008 0.40Y −0.00129 0.60Y −0.00719 0.80Y −0.026841.00Y −0.08390 [6th Surface (r6)] Height (|X|−|X0|)/{C0(N′-N) · f1}0.00Y −0.00000 0.20Y −0.00066 0.40Y −0.01070 0.60Y −0.05580 0.80Y−0.18492 1.00Y −0.48426 [11th Surface (r11)] Height (|X|−|X0|)/{C0(N′-N)· f2} 0.00Y −0.00000 0.20Y −0.00017 0.40Y −0.00282 0.60Y −0.01457 0.80Y−0.04772 1.00Y −0.12247 Example 5 [3rd Surface (r3)] Height(|X|−|X0|)/{C0(N′-N) · f1} 0.00Y −0.00000 0.20Y −0.00058 0.40Y −0.009380.60Y −0.04968 0.80Y −0.17281 1.00Y −0.49672 [12th Surface (r12)] Height(|X|−|X0|)/{C0(N′-N) · f2} 0.00Y 0.00000 0.20Y −0.00039 0.40Y −0.006300.60Y −0.03215 0.80Y −0.10366 1.00Y −0.26303

TABLE 19 The values corresponding to Conditions (15) and (17) inExamples 6 to 15 Example 6 [3rd Surface (r3)] Height(|X|−|X0|)/{C0(N′-N) · f1} 0.00Y −0.00000 0.20Y −0.00036 0.40Y −0.005850.60Y −0.03124 0.80Y −0.10983 1.00Y −0.31946 [12th Surface (r12)] Height(|X|−|X0|)/{C0(N′-N) · f2} 0.00Y 0.00000 0.20Y −0.00016 0.40Y −0.002660.60Y −0.01382 0.80Y −0.04620 1.00Y −0.12441 Example 7 [3rd Surface(r3)] Height (|X|−|X0|)/{C0(N′-N) · f1} 0.00Y −0.00000 0.20Y −0.000400.40Y −0.00645 0.60Y −0.03442 0.80Y −0.12249 1.00Y −0.36724 [14thSurface (r14)] Height (|X|−|X0|)/{C0(N′-N) · f3} 0.00Y 0.00000 0.20Y−0.00005 0.40Y −0.00072 0.60Y −0.00343 0.80Y −0.00979 1.00Y −0.02004Example 8 [1st Surface (r1)] Height (|X|−|X0|)/{C0(N′-N) · f1} 0.00Y−0.00000 0.20Y −0.00047 0.40Y −0.00762 0.60Y −0.04017 0.80Y −0.139751.00Y −0.40512 [14th Surface (r14)] Height (|X|−|X0|)/{C0(N′-N) · f3}0.00Y 0.00000 0.20Y −0.00007 0.40Y −0.00103 0.60Y −0.00497 0.80Y−0.01421 1.00Y −0.02846 Example 9 [3rd Surface (r3)] Height(|X|−|X0|)/{C0(N′-N) · f1} 0.00Y −0.00000 0.20Y −0.00034 0.40Y −0.005490.60Y −0.02824 0.80Y −0.09332 1.00Y −0.24896 [11th Surface (r11)] Height(|X|−|X0|)/{C0(N′-N) · f2} 0.00Y 0.00000 0.20Y −0.00086 0.40Y −0.014140.60Y −0.07574 0.80Y −0.26114 1.00Y −0.14147 Example 10 [1st Surface(r1)] Height (|X|−|X0|)/{C0(N′-N) · f1} 0.00Y −0.00000 0.20Y −0.000770.40Y −0.01256 0.60Y −0.06639 0.80Y −0.22928 1.00Y −0.65070 [14thSurface (r14)] Height (|X|−|X0|)/{C0(N′-N) · f3} 0.00Y 0.00000 0.20Y−0.00008 0.40Y −0.00129 0.60Y −0.00655 0.80Y −0.02065 1.00Y −0.04955Example 11 [3rd Surface (r3)] Height (|X|−|X0|)/{C0(N′-N) · f1} 0.00Y−0.00000 0.20Y −0.00041 0.40Y −0.00663 0.60Y −0.03428 0.80Y −0.114651.00Y −0.31309 [10th Surface (r10)] Height (|X|−|X0|)/{C0(N′-N) · f2}0.00Y 0.00000 0.20Y −0.00016 0.40Y −0.00260 0.60Y −0.01388 0.80Y−0.04736 1.00Y −0.12790 Example 12 [3rd Surface (r3)] Height(|X|−|X0|)/{C0(N′-N) · f1} 0.00Y −0.00000 0.20Y −0.00058 0.40Y −0.009400.60Y −0.04961 0.80Y −0.17667 1.00Y −0.53893 [12th Surface (r12)] Height(|X|−|X0|)/{C0(N′-N) · f2} 0.00Y 0.00000 0.20Y −0.00011 0.40Y −0.001820.60Y −0.00969 0.80Y −0.03330 1.00Y −0.09218 [15th Surface (r15)] Height(|X|−|X0|)/{C0(N′-N) · f3} 0.00Y 0.00000 0.20Y −0.00033 0.40Y −0.005020.60Y −0.02364 0.80Y −0.06629 1.00Y −0.13286 Example 13 [3rd Surface(r3)] Height (|X|−|X0|)/{C0(N′-N) · f1} 0.00Y −0.00000 0.20Y −0.000820.40Y −0.01333 0.60Y −0.07171 0.80Y −0.26196 1.00Y −0.82010 [12thSurface (r12)] Height (|X|−|X0|)/{C0(N′-N) · f2} 0.00Y 0.00000 0.20Y−0.00020 0.40Y −0.00328 0.60Y −0.01759 0.80Y −0.06132 1.00Y −0.17301[14th Surface (r14)] Height (|X|−|X0|)/{C0(N′-N) · f3} 0.00Y 0.000000.20Y −0.00020 0.40Y −0.00311 0.60Y −0.01525 0.80Y −0.04605 1.00Y−0.10564 [17th Surface (r17)] Height (|X|−|X0|)/{C0(N′-N) · f3} 0.00Y0.00000 0.20Y 0.00068 0.40Y 0.01090 0.60Y 0.05583 0.80Y 0.17801 1.00Y0.43402 Example 14 [3rd Surface (r3)] Height (|X|−|X0|)/{C0(N′-N) · f1}0.00Y −0.00000 0.20Y −0.00048 0.40Y −0.00802 0.60Y −0.04370 0.80Y−0.15559 1.00Y −0.44995 [12th Surface (r12)] Height (|X|−|X0|)/{C0(N′-N)· f2} 0.00Y 0.00000 0.20Y −0.00007 0.40Y −0.00110 0.60Y −0.00579 0.80Y−0.01922 1.00Y −0.04962 [15th Surface (r15)] Height (|X|−|X0|)/{C0(N′-N)· f3} 0.00Y 0.00000 0.20Y −0.00067 0.40Y −0.01051 0.60Y −0.05178 0.80Y−0.15744 1.00Y −0.36553

What is claimed is:
 1. A zoom lens system comprising, in order from anobject side: a first lens unit; a second lens unit having a positiveoptical power; and a third lens unit, wherein zooming is achieved bymoving at least two lens units so as to vary a distance between thefirst and second lens units and a distance between the second and thirdlens units, and wherein at least one of the lens elements included inthe lens units is a plastic lens element that fulfills the followingconditions: −0.8<Cp×(N′−N)/φW<0.8 −0.45<M3/M2<0.90 (where φT/φW>1.6)where Cp represents a curvature of the plastic lens element; φWrepresents an optical power of the entire zoom lens system at awide-angle end; N′ represents a refractive index of an object-sidemedium of an aspherical surface for d line; N represents a refractiveindex of an image-side medium of an aspherical surface for d line; M3represents an amount of movement of the third lens unit (where thedirection pointing to the object side is negative with respect to thewide-angle end); M2 represents an amount of movement of the second lensunit; and φT represents an optical power of the entire zoom lens systemat a telephoto end.
 2. The zoom lens system of claim 1 wherein saidfirst lens unit has a negative optical power.
 3. The zoom lens system ofclaim 1 wherein said second lens unit includes a positive lens elementand a negative lens element.
 4. The zoom lens system of claim 1 whereinsaid third lens unit has a positive optical power.
 5. The zoom lenssystem of claim 1 wherein said plastic lens element is contained in thefirst lens unit and fulfills the following conditions: |φP/φ1|<1.200.20<|φ1/φW|<0.70 where φP represents an optical power of the plasticlens element; φ1 represents an optical power of the first lens unit; andφT represents an optical power of the entire zoom lens system at atelephoto end.
 6. The zoom lens system of claim 5 wherein said firstlens unit has a negative optical power.
 7. The zoom lens system of claim6 wherein said first lens unit includes a positive lens element and anegative lens element.
 8. The zoom lens system of claim 5 wherein saidthird lens unit has a positive optical power.
 9. The zoom lens system ofclaim 1, wherein said plastic lens element is included in the secondlens unit and fulfills the following conditions: |φP/φ2|<2.50.25<φ2/φW<0.75 where φP represents an optical power of the plastic lenselement; and φ2 represents an optical power of the second lens unit. 10.The zoom lens system of claim 9 wherein said first lens unit has anegative optical power.
 11. The zoom lens system of claim 9 wherein saidsecond lens unit includes a positive lens element and a negative lenselement.
 12. The zoom lens system of claim 9 wherein said third lensunit has a positive optical power.
 13. The zoom lens system of claim 1wherein said plastic lens element is included in the third lens unit andfulfills the following conditions: −0.30<M3/M2<0.90 |φP/φ3|<1.700.1<φ3/φW<0.60 where φP represents an optical power of the plastic lenselement; and φ3 represents an optical power of the third lens unit. 14.The zoom lens system of claim 13 wherein said first lens unit has anegative optical power.
 15. The zoom lens system of claim 13 whereinsaid third lens unit has a positive optical power.
 16. The zoom lenssystem of claim 1, wherein at least one of the lens elements included inthe first lens unit and at least one of the lens elements included inthe second lens unit are plastic lens elements that fulfill thefollowing conditions:  −1.4<φPi/φW×hi<1.4 0.5<log(β2T/β2W)/logZ<2.2where φPi represents an optical power of an ith plastic lens element; hirepresents a height of incidence at which a paraxial ray enters anobject-side surface of the ith plastic lens element at a telephoto end,assuming that initial values of a converted inclination α1 and a heighth1, for paraxial tracing, are 0 and 1, respectively; β2W represents alateral magnification of the second lens unit at the wide-angle end; β2Trepresents a lateral magnification of the second lens unit at thetelephoto end; Z represents a zoom ratio; and log represents a naturallogarithm.
 17. The zoom lens system of claim 16 wherein said first lensunit has a negative optical power.
 18. The zoom lens system of claim 16wherein said third lens unit has a positive optical power.
 19. The zoomlens system as claimed in claim 1, wherein at least one of the lenselements included in the first lens unit and at least one of the lenselements included in the third lens element are plastic lens elementsthat fulfill the following conditions: −1.4<φPi/φW×hi<1.4−1.2<log(β3T/β3W)/logZ<0.5 where φPi represents an optical power of anith plastic lens element; hi represents a height of incidence at which aparaxial ray enters an object-side surface of the ith plastic lenselement at a telephoto end, assuming that initial values of a convertedinclination al and a height hi, for paraxial tracing, are 0 and 1,respectively; β3W represents a lateral magnification of the third lensunit at the wide-angle end; β3T represents a lateral magnification ofthe third lens unit at the telephoto end; Z represents a zoom ratio; andlog represents a natural logarithm.
 20. The zoom lens system of claim 19wherein said first lens unit has a negative optical power.
 21. The zoomlens system of claim 19 wherein said second lens unit includes apositive lens element and a negative lens element.
 22. The zoom lenssystem of claim 19 wherein said third lens unit has a positive opticalpower.
 23. The zoom lens system of claim 1, wherein at least one of thelens elements included in the second lens unit and at least one of thelens elements included in the third lens unit are plastic lens elementsthat fulfill the following conditions: −1.4<φPi/φW×hi<1.4−0.75<log(β3T/β3W)/log(β2T/β2W)<0.65 where φPi represents an opticalpower of an ith plastic lens element; hi represents a height ofincidence at which a paraxial ray enters an object-side surface of theith plastic lens element at a telephoto end, assuming that initialvalues of a converted inclination acl and a height hi, for paraxialtracing, are 0 and 1, respectively; β2W represents a lateralmagnification of the second lens unit at the wide-angle end; β2Trepresents a lateral magnification of the second lens unit at thetelephoto end; β3W represents a lateral magnification of the third lensunit at the wide-angle end; β3T represents a lateral magnification ofthe third lens unit at the telephoto end; and log represents a naturallogarithm.
 24. The zoom lens system of claim 23 wherein said first lensunit has a negative optical power.
 25. The zoom lens system of claim 23wherein said second lens unit includes a positive lens element and anegative lens element.
 26. The zoom lens system of claim 23 wherein saidthird lens unit has a positive optical power.
 27. The zoom lens systemcomprising, in order from an object side: a first lens unit; a secondlens unit having a positive optical power; and a third lens unit,wherein zooming is achieved by varying a distance between the first andsecond lens units and a distance between the second and third lensunits, and wherein at least one of the lens elements included in thesecond lens unit is a plastic lens element that fulfills the followingconditions: |φP/φ2|<2.5 0.25<φ2/φW<0.75  where φP represents an opticalpower of the plastic lens element; φ2 represents an optical power of thesecond lens unit; and φW represents an optical power of the entire zoomlens system at a wide-angle end.
 28. A zoom lens system comprising, inorder from an object side: a first lens unit; a second lens unit havinga positive optical power; and a third lens unit, wherein zooming isachieved by moving at least two lens units so as to vary a distancebetween the first and second lens units and a distance between thesecond and third lens units, and wherein at least one of the lenselements included in the third lens unit is a plastic lens element thatfulfill the following conditions: −0.30<M3/M2<0.90 |φP/φ3|<1.700.1<φ3/φW<0.60  where M3 represents an amount of movement of the thirdlens unit (the direction pointing to the object side is negative withrespect to a wide-angle end); M2 represents an amount of movement of thesecond lens unit; φP represents an optical power of the plastic lenselement; φ3 represents an optical power of the third lens unit; and φWrepresents an optical power of the entire zoom lens system at awide-angle end.
 29. A zoom lens system comprising, in order from anobject side: a first lens unit; a second lens unit having a positiveoptical power; and a third lens unit, wherein zooming is achieved bymoving at least two lens units so as to vary a distance between thefirst and second lens units and a distance between the second and thirdlens units, and wherein at least one of the lens elements included inthe first lens unit and at least one of the lens elements included inthe second lens unit are plastic lens element that fulfills thefollowing conditions: −1.4<φPi/φW×hi<1.4 0.5<log(β2T/β2W)/logZ<2.2 where φPi represents an optical power of an ith plastic lens element;φW represents an optical power of the entire zoom lens system at awide-angle end; hi represents a height of incidence at which a paraxialray enters an object-side surface of the ith plastic lens element at atelephoto end, assuming that initial values of a converted inclinationα1 and a height h1, for paraxial tracing, are 0 and 1, respectively; β2Wrepresents a lateral magnification of the second lens unit at thewide-angle end; β2T represents a lateral magnification of the secondlens unit at the telephoto end; Z represents a zoom ratio; and logrepresents a natural logarithm.
 30. A zoom lens system comprising, inorder from an object side: a first lens unit; a second lens unit havinga positive optical power; and a third lens unit, wherein zooming isachieved by moving at least two lens units so as to vary a distancebetween the first and second lens units and a distance between thesecond and third lens units, and wherein at least one of the lenselements included in the first lens unit and at least one of the lenselements included in the third lens unit are plastic lens element thatfulfill the following conditions:  −1.4<φPi/φW×hi<1.4−1.2<log(β3T/β3W)/logZ<0.5  where φPi represents an optical power of anith plastic lens element; φW represents an optical power of the entirezoom lens system at a wide-angle end; hi represents a height ofincidence at which a paraxial ray enters an object-side surface of theith plastic lens element at a telephoto end, assuming that initialvalues of a converted inclination α1 and a height h1, for paraxialtracing, are 0 and 1, respectively; β3W represents a lateralmagnification of the third lens unit at the wide-angle end; β3Trepresents a lateral magnification of the third lens unit at thetelephoto end; Z represents a zoom ratio; and log represents a naturallogarithm.
 31. A zoom lens system comprising, in order from an objectside: a first lens unit; a second lens unit having a positive opticalpower; and a third lens unit having a positive optical power, whereinzooming is achieved by moving at least two lens units so as to vary adistance between the first and second lens units and a distance betweenthe second and third lens units, and wherein at least one of the lenselements included in the second lens unit and at least one of the lenselements included in the third lens unit are plastic lens elements thatfulfill the following conditions: −1.4<φPi/φW×hi<1.4−0.75<log(β3T/β3W)/log(β2T/β2W)<0.65  where φPi represents an opticalpower of an ith plastic lens element; φW represents an optical power ofthe entire zoom lens system at a wide-angle end; hi represents a heightof incidence at which a paraxial ray enters an object-side surface ofthe ith plastic lens element at a telephoto end, assuming that initialvalues of a converted inclination α1 and a height h1, for paraxialtracing, are 0 and 1, respectively; β2W represents a lateralmagnification of the second lens unit at the wide-angle end; β2Trepresents a lateral magnification of the second lens unit at thetelephoto end; β3W represents a lateral magnification of the third lensunit at the wide-angle end; β3T represents a lateral magnification ofthe third lens unit at the telephoto end; and log represents a naturallogarithm.
 32. A digital camera comprising a zoom lens system, a lowpass filter and an image sensor, wherein said zoom lens system includes,in order from the object side thereof: a first lens unit; a second lensunit having a positive optical power; and a third lens unit, whereinzooming is achieved by moving at least two lens units so as to vary adistance between the first and second lens units and a distance betweenthe second and third lens units, and wherein at least one of the lenselements included in the lens units is a plastic lens element thatfulfills the following conditions: −0.8<Cp×(N′−N)/φW<0.8−0.45<M3/M2<0.90(where φT/φW>1.6)  where Cp represents a curvature ofthe plastic lens element; φW represents an optical power of the entirezoom lens system at a wide-angle end; N′ represents a refractive indexof an object-side medium of an aspherical surface for d line; Nrepresents a refractive index of an image-side medium of an asphericalsurface for d line; M3 represents an amount of movement of the thirdlens unit (where the direction pointing to the object side is negativewith respect to the wide-angle end); M2 represents an amount of movementof the second lens unit; and φT represents an optical power of theentire zoom lens system at a telephoto end.
 33. The digital camera ofclaim 32, wherein said first lens unit has a negative optical power. 34.The digital camera of claim 32, wherein said second lens unit includes apositive lens element and a negative lens element.
 35. The digitalcamera of claim 32, wherein said third lens unit has a positive opticalpower.
 36. The digital camera of claim 32, wherein said plastic lenselement is contained in the first lens unit and fulfills the followingconditions: |φP/φ1|<1.20 0.20<|φ1/φW|<0.70 where φP represents anoptical power of the plastic lens element; φ1 represents an opticalpower of the first lens unit; and φT represents an optical power of theentire zoom lens system at a telephoto end.
 37. The digital camera ofclaim 36, wherein said first lens unit has a negative optical power. 38.The digital camera of claim 37, wherein said first lens unit includes apositive lens element and a negative lens element.
 39. The digitalcamera of claim 36, wherein said third lens unit has a positive opticalpower.
 40. The digital camera of claim 32, wherein said plastic lenselement is included in the second lens unit and fulfills the followingconditions: |φP/φ2|<2.5 0.25<φ2/φW<0.75 where φP represents an opticalpower of the plastic lens element; and φ2 represents an optical power ofthe second lens unit.
 41. The digital camera of claim 40, wherein saidfirst lens unit has a negative optical power.
 42. The digital camera ofclaim 40, wherein said second lens unit includes a positive lens elementand a negative lens element.
 43. The digital camera of claim 40, whereinsaid third lens unit has a positive optical power.
 44. The zoom lenssystem of claim 32 wherein said plastic lens is included in the thirdlens unit and fulfills the following conditions: −0.30<M3/M2<0.90|φP/φ3|<1.70 0.1<φ3/φW<0.60 where φP represents an optical power of theplastic lens element; and φ3 represents an optical power of the thirdlens unit.
 45. The digital camera of claim 44, wherein said first lensunit has a negative optical power.
 46. The digital camera of claim 44,wherein said third lens unit has a positive optical power.
 47. Thedigital camera of claim 32, wherein at least one of the lens elementsincluded in the first lens unit and at least one of the lens elementsincluded in the second lens unit are plastic lens elements that fulfillthe following conditions: −1.4<φPi/φW×hi<1.4 0.5<log(β2T/β2W)/logZ<2.2where φPi represents an optical power of an ith plastic lens element; hirepresents a height of incidence at which a paraxial ray enters anobject-side surface of the ith plastic lens element at a telephoto end,assuming that initial values of a converted inclination α1 and a heighth1, for paraxial tracing, are 0 and 1, respectively; β2W represents alateral magnification of the second lens unit at the wide-angle end; β2Trepresents a lateral magnification of the second lens unit at thetelephoto end; Z represents a zoom ratio; and log represents a naturallogarithm.
 48. The digital camera of claim 47, wherein said first lensunit has a negative optical power.
 49. The digital camera of claim 47,wherein said third lens unit has a positive optical power.
 50. Thedigital camera of claim 32, wherein at least one of the lens elementsincluded in the first lens unit and at least one of the lens elementsincluded in the third lens element are plastic lens elements thatfulfill the following conditions: −1.4<φPi/φW×hi<1.4−1.2<log(β3T/β3W)/logZ<0.5 where φPi represents an optical power of anith plastic lens element; hi represents a height of incidence at which aparaxial ray enters an object-side surface of the ith plastic lenselement at a telephoto end, assuming that initial values of a convertedinclination α1 and a height h1, for paraxial tracing, are 0 and 1,respectively; β3W represents a lateral magnification of the third lensunit at the wide-angle end; β3T represents a lateral magnification ofthe third lens unit at the telephoto end; Z represents a zoom ratio; andlog represents a natural logarithm.
 51. The digital camera of claim 50,wherein said first lens unit has a negative optical power.
 52. Thedigital camera of claim 50, wherein said second lens unit includes apositive lens element and a negative lens element.
 53. The digitalcamera of claim 50, wherein said third lens unit has a positive opticalpower.
 54. The digital camera of claim 32, wherein at least one of thelens elements included in the second lens unit and at least one of thelens elements included in the third lens unit are plastic lens elementsthat fulfill the following conditions: −1.4<φPi/φW×hi<1.4−0.75<log(β3T/β3W)/log(β2T/β2W)<0.65 where φPi represents an opticalpower of an ith plastic lens element; hi represents a height ofincidence at which a paraxial ray enters an object-side surface of theith plastic lens element at a telephoto end, assuming that initialvalues of a converted inclination α1 and a height h1, for paraxialtracing, are 0 and 1, respectively; β2W represents a lateralmagnification of the second lens unit at the wide-angle end; β2Trepresents a lateral magnification of the second lens unit at thetelephoto end; β3W represents a lateral magnification of the third lensunit at the wide-angle end; β3T represents a lateral magnification ofthe third lens unit at the telephoto end; and log represents a naturallogarithm.
 55. The digital camera of claim 54, wherein said first lensunit has a negative optical power.
 56. The digital camera of claim 54,wherein said second lens unit includes a positive lens element and anegative lens element.
 57. The digital camera of claim 54, wherein saidthird lens unit has a positive optical power.